scsi: mpt3sas: Remove NULL check before freeing function

Fix the following coccicheck warning:

drivers/scsi/mpt3sas/mpt3sas_base.c:4906:3-19: WARNING: NULL check
before some freeing functions is not needed.

Link: https://lore.kernel.org/r/20200418095850.34883-1-yanaijie@huawei.comReported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/mpt3sas/mpt3sas_base.c

@@ -4887,8 +4887,7 @@ _base_release_memory_pools(struct MPT3SAS_ADAPTER *ioc)
 					ioc->pcie_sg_lookup[i].pcie_sgl,
 					ioc->pcie_sg_lookup[i].pcie_sgl_dma);
 		}
-		if (ioc->pcie_sgl_dma_pool)
-			dma_pool_destroy(ioc->pcie_sgl_dma_pool);
+		dma_pool_destroy(ioc->pcie_sgl_dma_pool);
 	}
 
 	if (ioc->config_page) {