scsi: qla2xxx: Remove superfluous memset()

Fixes coccicheck warning:

./drivers/scsi/qla2xxx/qla_mbx.c:4928:15-33: WARNING: dma_alloc_coherent use in els_cmd_map 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/1596079918-41115-3-git-send-email-liheng40@huawei.com


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