scsi: megaraid_sas: Replace one-element array with flexible-array member in MR_PD_CFG_SEQ_NUM_SYNC

One-element arrays are deprecated, and we are replacing them with flexible
array members instead. So, replace one-element array with flexible-array
member in struct MR_PD_CFG_SEQ_NUM_SYNC and refactor the rest of the code
accordingly.

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE routines
on memcpy() and help us make progress towards globally enabling
-fstrict-flex-arrays [0].

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Link: Link: https://reviews.llvm.org/D126864 [0]
Link: https://lore.kernel.org/r/78e9261591db072b67fcf49f0216d7046a67ca6d.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>