[PATCH][next] scsi: megaraid_sas: Avoid a couple -Wflex-array-member-not-at-end warnings

["Gustavo A. R. Silva" <gustavoars@kernel.org>]

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Use the new TRAILING_OVERLAP() helper to fix the following warnings:

drivers/scsi/megaraid/megaraid_sas_fusion.h:1153:31: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]
drivers/scsi/megaraid/megaraid_sas_fusion.h:1198:32: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

This helper creates a union between a flexible-array member (FAM)
and a set of MEMBERS that would otherwise follow it --in this case
`struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES_DYN]` and
`struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES]` in the
corresponding structures.

This overlays the trailing members onto the FAM (struct MR_LD_SPAN_MAP
ldSpanMap[];) while keeping the FAM and the start of MEMBERS aligned.

The static_assert() ensures this alignment remains, and it's intentionally
placed inmediately after `struct virtnet_info` --no blank line in between).

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 drivers/scsi/megaraid/megaraid_sas_fusion.h | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/megaraid/megaraid_sas_fusion.h b/drivers/scsi/megaraid/megaraid_sas_fusion.h
index b677d80e5874..ddeea0ee2834 100644
--- a/drivers/scsi/megaraid/megaraid_sas_fusion.h
+++ b/drivers/scsi/megaraid/megaraid_sas_fusion.h
@@ -1150,9 +1150,13 @@ typedef struct LOG_BLOCK_SPAN_INFO {
 } LD_SPAN_INFO, *PLD_SPAN_INFO;
 
 struct MR_FW_RAID_MAP_ALL {
-	struct MR_FW_RAID_MAP raidMap;
-	struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES];
+	/* Must be last --ends in a flexible-array member. */
+	TRAILING_OVERLAP(struct MR_FW_RAID_MAP, raidMap, ldSpanMap,
+		struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES];
+	);
 } __attribute__ ((packed));
+static_assert(offsetof(struct MR_FW_RAID_MAP_ALL, raidMap.ldSpanMap) ==
+	      offsetof(struct MR_FW_RAID_MAP_ALL, ldSpanMap));
 
 struct MR_DRV_RAID_MAP {
 	/* total size of this structure, including this field.
@@ -1194,10 +1198,13 @@ struct MR_DRV_RAID_MAP {
  * And it is mainly for code re-use purpose.
  */
 struct MR_DRV_RAID_MAP_ALL {
-
-	struct MR_DRV_RAID_MAP raidMap;
-	struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES_DYN];
+	/* Must be last --ends in a flexible-array member. */
+	TRAILING_OVERLAP(struct MR_DRV_RAID_MAP, raidMap, ldSpanMap,
+		struct MR_LD_SPAN_MAP ldSpanMap[MAX_LOGICAL_DRIVES_DYN];
+	);
 } __packed;
+static_assert(offsetof(struct MR_DRV_RAID_MAP_ALL, raidMap.ldSpanMap) ==
+	      offsetof(struct MR_DRV_RAID_MAP_ALL, ldSpanMap));
 
 
 
-- 
2.43.0