ASoC: apple: mca: Annotate struct mca_data with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct mca_data.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Martin Povišer <[e-mail]>
Cc: Liam Girdwood <[e-mail]>
Cc: Mark Brown <[e-mail]>
Cc: Jaroslav Kysela <[e-mail]>
Cc: Takashi Iwai <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Kees Cook <[e-mail]>
Reviewed-by: "Gustavo A. R. Silva" <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

sound/soc/apple/mca.c

···
 	struct mutex port_mutex;
 
 	int nclusters;
-	struct mca_cluster clusters[];
+	struct mca_cluster clusters[] __counted_by(nclusters);
 };
 
 static void mca_modify(struct mca_cluster *cl, int regoffset, u32 mask, u32 val)