scsi: mpi3mr: Drop unnecessary volatile from __iomem pointers

The volatile qualifier is redundant for __iomem pointers.

Cleaned up usage in mpi3mr_writeq() and sysif_regs pointer as per
Upstream compliance.

Signed-off-by: Ranjan Kumar <ranjan.kumar@broadcom.com>
Link: https://lore.kernel.org/r/20250627194539.48851-3-ranjan.kumar@broadcom.com


Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>