ath: Replace zero-length arrays with flexible-array members

There is a regular need in the kernel to provide a way to declare
having a dynamically sized set of trailing elements in a structure.
Kernel code should always use “flexible array members”[1] for these
cases. The older style of one-element or zero-length arrays should
no longer be used[2].

[1] https://en.wikipedia.org/wiki/Flexible_array_member
[2] https://www.kernel.org/doc/html/v5.16/process/deprecated.html#zero-length-and-one-element-arrays

Link: https://github.com/KSPP/linux/issues/78
Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Signed-off-by: Kalle Valo <[e-mail]>
Link: https://lore.kernel.org/r/20220216194915.GA904081@embeddedor

drivers/net/wireless/ath/spectral_common.h

···
 	u8 avgpwr_db;
 	u8 max_exp;
 
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 struct fft_sample_ath11k {
···
 	__be32 tsf;
 	__be32 noise;
 
-	u8 data[0];
+	u8 data[];
 } __packed;
 
 #endif /* SPECTRAL_COMMON_H */