rbd: use gfp_flags parameter in rbd_header_from_disk()

We should use the gfp_flags that the caller specified instead of
GFP_KERNEL here.

There is only one caller and it uses GFP_KERNEL, so this change is
just a cleanup and doesn't change how the code works.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Alex Elder <elder@dreamhost.com>

drivers/block/rbd.c

@@ -506,11 +506,11 @@ static int rbd_header_from_disk(struct rbd_image_header *header,
 	header->snap_names_len = le64_to_cpu(ondisk->snap_names_len);
 	if (snap_count) {
 		header->snap_names = kmalloc(header->snap_names_len,
-					     GFP_KERNEL);
+					     gfp_flags);
 		if (!header->snap_names)
 			goto err_snapc;
 		header->snap_sizes = kmalloc(snap_count * sizeof(u64),
-					     GFP_KERNEL);
+					     gfp_flags);
 		if (!header->snap_sizes)
 			goto err_names;
 	} else {