scsi: qla2xxx: Replace one-element array with DECLARE_FLEX_ARRAY() helper

scsi: qla2xxx: Replace one-element array with DECLARE_FLEX_ARRAY() helper

One-element arrays as fake flex arrays are deprecated and we are moving
towards adopting C99 flexible-array members, instead. So, replace
one-element array declaration in struct ct_sns_gpnft_rsp, which is
ultimately being used inside a union:

drivers/scsi/qla2xxx/qla_def.h:
3240 struct ct_sns_gpnft_pkt {
3241         union {
3242                 struct ct_sns_req req;
3243                 struct ct_sns_gpnft_rsp rsp;
3244         } p;
3245 };

Refactor the rest of the code, accordingly.

This issue was found with the help of Coccinelle.

Link: https://github.com/KSPP/linux/issues/245
Link: https://github.com/KSPP/linux/issues/193
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/ZH+/rZ1R1cBjIxjS@work
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>