ext4: use ext4_warning() for sb_getblk failure

Out of memory should not be considered as critical errors; so replace
ext4_error() with ext4_warnig().

Signed-off-by: Wang Shilong <wshilong@ddn.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index aa52d87..e5d6ee6 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -426,9 +426,9 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 	}
 	bh = sb_getblk(sb, bitmap_blk);
 	if (unlikely(!bh)) {
-		ext4_error(sb, "Cannot get buffer for block bitmap - "
-			   "block_group = %u, block_bitmap = %llu",
-			   block_group, bitmap_blk);
+		ext4_warning(sb, "Cannot get buffer for block bitmap - "
+			     "block_group = %u, block_bitmap = %llu",
+			     block_group, bitmap_blk);
 		return ERR_PTR(-ENOMEM);
 	}