scsi: mpt3sas: Convert to flexible arrays

This converts to a flexible array instead of the old-style 1-element
arrays. The existing code already did the correct math for finding the size
of the resulting flexible array structure, so there is no binary
difference.

The other two structures converted to use flexible arrays appear to have no
users at all.

Link: https://lore.kernel.org/r/20220201223948.1455637-1-keescook@chromium.org


Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>