[PATCH v2][next] ALSA: firewire-lib: Avoid -Wflex-array-member-not-at-end warning

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

Use the `DEFINE_FLEX()` helper for an on-stack definition of a
flexible structure where the size of the flexible-array member
is known at compile-time, and refactor the rest of the code,
accordingly.

So, with these changes, fix the following warning:
sound/firewire/amdtp-stream.c:1184:46: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Link: https://github.com/KSPP/linux/issues/202
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
Changes in v2:
 - Use DEFINE_FLEX() helper instead of a new tagged struct.

v1:
 - Link: https://lore.kernel.org/linux-hardening/d3a764eb76909b16b8a22d9ff530e5edf0e59e6b.1709658886.git.gustavoars@kernel.org/

 sound/firewire/amdtp-stream.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/sound/firewire/amdtp-stream.c b/sound/firewire/amdtp-stream.c
index c9f153f85ae6..d35d0a420ee0 100644
--- a/sound/firewire/amdtp-stream.c
+++ b/sound/firewire/amdtp-stream.c
@@ -1180,13 +1180,11 @@ static void process_rx_packets(struct fw_iso_context *context, u32 tstamp, size_
 		(void)fw_card_read_cycle_time(fw_parent_device(s->unit)->card, &curr_cycle_time);
 
 	for (i = 0; i < packets; ++i) {
-		struct {
-			struct fw_iso_packet params;
-			__be32 header[CIP_HEADER_QUADLETS];
-		} template = { {0}, {0} };
+		DEFINE_FLEX(struct fw_iso_packet, template, header,
+			    header_length, CIP_HEADER_QUADLETS);
 		bool sched_irq = false;
 
-		build_it_pkt_header(s, desc->cycle, &template.params, pkt_header_length,
+		build_it_pkt_header(s, desc->cycle, template, pkt_header_length,
 				    desc->data_blocks, desc->data_block_counter,
 				    desc->syt, i, curr_cycle_time);
 
@@ -1198,7 +1196,7 @@ static void process_rx_packets(struct fw_iso_context *context, u32 tstamp, size_
 			}
 		}
 
-		if (queue_out_packet(s, &template.params, sched_irq) < 0) {
+		if (queue_out_packet(s, template, sched_irq) < 0) {
 			cancel_stream(s);
 			return;
 		}
-- 
2.34.1