scsi: mvsas: Remove superfluous memset()

Fixes coccicheck warning:

./drivers/scsi/mvsas/mv_init.c:244:11-29: WARNING: dma_alloc_coherent use in mvi -> tx already zeroes out memory,  so memset is not needed
./drivers/scsi/mvsas/mv_init.c:250:15-33: WARNING: dma_alloc_coherent use in mvi -> rx_fis already zeroes out memory,  so memset is not needed
./drivers/scsi/mvsas/mv_init.c:256:11-29: WARNING: dma_alloc_coherent use in mvi -> rx already zeroes out memory,  so memset is not needed
./drivers/scsi/mvsas/mv_init.c:265:13-31: WARNING: dma_alloc_coherent use in mvi -> slot already zeroes out memory,  so memset is not needed

dma_alloc_coherent() already zeroes out memory so memset() is not needed.

Link: https://lore.kernel.org/r/1596078235-54002-1-git-send-email-liheng40@huawei.com


Signed-off-by: Li Heng <liheng40@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>