Fix memset() accessing out of range address when reply_queue count is less
than RDPQ_MAX_INDEX_IN_ONE_CHUNK (i.e. 16) in non-RDPQ mode.

In non-RDPQ mode, the driver allocates a single contiguous pool of size
reply_queue's count * reqly_post_free_sz. But the driver is always
memsetting this pool with size 16 * reqly_post_free_sz. If reply queue
count is less than 16 (i.e. when MSI-X vectors enabled < 16), the driver is
accessing out of range address and this results in 'BUG: unable to handle
kernel paging request at fff0x...x' bug.

Make driver use dma_pool_zalloc() API to allocate and zero the pool.

Link: https://lore.kernel.org/r/20200528145617.27252-1-suganath-prabu.subramani@broadcom.com
Fixes: 8012209e ("scsi: mpt3sas: Handle RDPQ DMA allocation in same 4G region")
Signed-off-by: Suganath Prabu S <suganath-prabu.subramani@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>