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

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_DRV_RAID_MAP and refactor the the rest of the code
accordingly.

This helps with the ongoing efforts to tighten the FORTIFY_SOURCE routines
on memcpy().

Link: https://github.com/KSPP/linux/issues/79
Link: https://github.com/KSPP/linux/issues/109
Link: https://lore.kernel.org/r/4495ce170c8ef088a10f1abe0e7c227368f43242.1660592640.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>
Enhanced-by: Kees Cook <keescook@chromium.org> # Change in struct MR_FW_RAID_MAP_ALL