[PATCH][next] ASoC: soc-topology: Avoid -Wflex-array-member-not-at-end warning

["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 __TRAILING_OVERLAP() helper to fix the following warning:

sound/soc/soc-topology-test.c:136:38: 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. This overlays
the trailing members onto the FAM while preserving the original
memory layout.

Lastly, the static_assert() ensures the alignment between the FAM
and struct snd_soc_tplg_hdr pcm_header; is not inadvertently changed,
and it's intentionally placed immediately after the related structure
(that is, no blank line in between).

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
 sound/soc/soc-topology-test.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/sound/soc/soc-topology-test.c b/sound/soc/soc-topology-test.c
index c8f2ec29e970..ef6725613b01 100644
--- a/sound/soc/soc-topology-test.c
+++ b/sound/soc/soc-topology-test.c
@@ -133,10 +133,15 @@ static struct tplg_tmpl_001 tplg_tmpl_empty = {
 
 struct tplg_tmpl_002 {
 	struct snd_soc_tplg_hdr header;
-	struct snd_soc_tplg_manifest manifest;
-	struct snd_soc_tplg_hdr pcm_header;
-	struct snd_soc_tplg_pcm pcm;
+
+	/* Must be last as it ends in a flexible-array member. */
+	__TRAILING_OVERLAP(struct snd_soc_tplg_manifest, manifest, priv.data, __packed,
+		struct snd_soc_tplg_hdr pcm_header;
+		struct snd_soc_tplg_pcm pcm;
+	);
 } __packed;
+static_assert(offsetof(struct tplg_tmpl_002, manifest.priv.data) ==
+	      offsetof(struct tplg_tmpl_002, pcm_header));
 
 static struct tplg_tmpl_002 tplg_tmpl_with_pcm = {
 	.header = {
-- 
2.51.0