scsi: megaraid_sas: Use struct_size() in code related to struct MR_PD_CFG_SEQ_NUM_SYNC

scsi: megaraid_sas: Use struct_size() in code related to struct MR_PD_CFG_SEQ_NUM_SYNC

Prefer struct_size() over open-coded versions of idiom:

        sizeof(struct-with-flex-array) + sizeof(type-of-flex-array) * count

where count is the max number of items the flexible array is supposed to
have.

Link: https://github.com/KSPP/linux/issues/160
Link: https://lore.kernel.org/r/b215f4760f0e8fbe5fc35be20f2487e89924424d.1660592640.git.gustavoars@kernel.org
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>