NVMe: handle allocation failure in nvme_map_user_pages()

We should return here and avoid a NULL dereference.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
diff --git a/drivers/block/nvme.c b/drivers/block/nvme.c
index 6c0eb76..064e86a 100644
--- a/drivers/block/nvme.c
+++ b/drivers/block/nvme.c
@@ -1044,6 +1044,8 @@
 	offset = offset_in_page(addr);
 	count = DIV_ROUND_UP(offset + length, PAGE_SIZE);
 	pages = kcalloc(count, sizeof(*pages), GFP_KERNEL);
+	if (!pages)
+		return ERR_PTR(-ENOMEM);
 
 	err = get_user_pages_fast(addr, count, 1, pages);
 	if (err < count) {