scsi: mpt3sas: Convert to flexible arrays

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.

Cc: Sathya Prakash <sathya.prakash@broadcom.com>
Cc: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Cc: Suganath Prabu Subramani <suganath-prabu.subramani@broadcom.com>
Cc: "James E.J. Bottomley" <jejb@linux.ibm.com>
Cc: "Martin K. Petersen" <martin.petersen@oracle.com>
Cc: MPT-FusionLinux.pdl@broadcom.com
Cc: linux-scsi@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>