NVMe: Remove check for null

Checking fails static analysis due to additional arithmetic prior to
the NULL check. Mapping doesn't return NULL here anyway, so removing
the check.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/block/nvme-core.c

@@ -517,8 +517,6 @@ static void nvme_dif_remap(struct request *req,
 		return;
 
 	pmap = kmap_atomic(bip->bip_vec->bv_page) + bip->bip_vec->bv_offset;
-	if (!pmap)
-		return;
 
 	p = pmap;
 	virt = bip_get_seed(bip);