scsi: pmcraid: Replace dma_pool_malloc with dma_pool_zalloc

Replace dma_pool_malloc with dma_pool_zalloc to make the code more concise
in pmcraid_allocate_control_blocks() function.

Link: https://lore.kernel.org/r/1587197241-274646-1-git-send-email-wubo40@huawei.com


Signed-off-by: Wu Bo <wubo40@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>