scsi: mpt3sas: fix header path in ioctl documentation

MPT2_MAGIC_NUMBER as well as drivers/scsi/mpt2sas/mpt2sas_ctl.h were
removed to reuse mpt3sas code since commit 09ec55ed ("mpt2sas: Remove
.c and .h files from mpt2sas driver").

Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@osnexus.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>