scsi: qla2xxx: Replace vmalloc + memset with vzalloc

Use vzalloc instead of using vmalloc to allocate memory and then zeroing it
with memset.  This simplifies the code.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Acked-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>