ext4: fix return-value types in several function comments

The documentation comments for ext4_read_block_bitmap_nowait and
ext4_read_inode_bitmap describe them as returning NULL on error, but
they return an ERR_PTR on error; update the documentation to match.

The documentation comment for ext4_wait_block_bitmap describes it as
returning 1 on error, but it returns -errno on error; update the
documentation to match.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Reviewed-by: Ritesh Harani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/60a3f4996f4932c45515aaa6b75ca42f2a78ec9b.1585512514.git.josh@joshtriplett.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/balloc.c

@@ -410,7 +410,7 @@ verified:
  * Read the bitmap for a given block_group,and validate the
  * bits for block/inode/inode tables are set in the bitmaps
  *
- * Return buffer_head on success or NULL in case of failure.
+ * Return buffer_head on success or an ERR_PTR in case of failure.
  */
 struct buffer_head *
 ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
@@ -502,7 +502,7 @@ out:
 	return ERR_PTR(err);
 }
 
-/* Returns 0 on success, 1 on error */
+/* Returns 0 on success, -errno on error */
 int ext4_wait_block_bitmap(struct super_block *sb, ext4_group_t block_group,
 			   struct buffer_head *bh)
 {

fs/ext4/ialloc.c

@@ -113,7 +113,7 @@ verified:
  * Read the inode allocation bitmap for a given block_group, reading
  * into the specified slot in the superblock's bitmap cache.
  *
- * Return buffer_head of bitmap on success or NULL.
+ * Return buffer_head of bitmap on success, or an ERR_PTR on error.
  */
 static struct buffer_head *
 ext4_read_inode_bitmap(struct super_block *sb, ext4_group_t block_group)