scsi: mptfusion: remove set, but not used, variables

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/message/fusion/mptspi.c: In function 'mptspi_writeIOCPage4':
drivers/message/fusion/mptspi.c:262:9: warning:
 variable 'frameOffset' set but not used [-Wunused-but-set-variable]

drivers/message/fusion/mptspi.c:261:9: warning:
 variable 'req_idx' set but not used [-Wunused-but-set-variable]

They're never used and can be removed.

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