Use vzalloc instead of vmalloc followed by memset 0.

Generated-by: scripts/coccinelle/api/alloc/kzalloc-simple.cocci
Suggested-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Himanshu Jha <himanshujha199640@gmail.com>
Acked-by: Anil Gurumurthy <anil.gurumurthy@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>