scsi: megaraid_sas: remove set but not used variable 'sge_sz'

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

drivers/scsi/megaraid/megaraid_sas_base.c: In function megasas_create_frame_pool:
drivers/scsi/megaraid/megaraid_sas_base.c:4124:6: warning: variable sge_sz set but not used [-Wunused-but-set-variable]

It's not used any more since commit 200aed58 ("megaraid_sas: endianness
related bug fixes and code optimization")

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Sumit Saxena <sumit.saxena@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>