ext4: add missed brelse in ext4_free_blocks_simple

Release bitmap buffer_head we got if error occurs.
Besides, this patch remove unused assignment to err.
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20230303172120.3800725-8-shikemeng@huaweicloud.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/mballoc.c

@@ -5849,13 +5849,12 @@ static void ext4_free_blocks_simple(struct inode *inode, ext4_fsblk_t block,
 	ext4_get_group_no_and_offset(sb, block, &group, &blkoff);
 	bitmap_bh = ext4_read_block_bitmap(sb, group);
 	if (IS_ERR(bitmap_bh)) {
-		err = PTR_ERR(bitmap_bh);
 		pr_warn("Failed to read block bitmap\n");
 		return;
 	}
 	gdp = ext4_get_group_desc(sb, group, &gdp_bh);
 	if (!gdp)
-		return;
+		goto err_out;
 
 	for (i = 0; i < count; i++) {
 		if (!mb_test_bit(blkoff + i, bitmap_bh->b_data))
@@ -5864,7 +5863,7 @@ static void ext4_free_blocks_simple(struct inode *inode, ext4_fsblk_t block,
 	mb_clear_bits(bitmap_bh->b_data, blkoff, count);
 	err = ext4_handle_dirty_metadata(NULL, NULL, bitmap_bh);
 	if (err)
-		return;
+		goto err_out;
 	ext4_free_group_clusters_set(
 		sb, gdp, ext4_free_group_clusters(sb, gdp) +
 		count - already_freed);
@@ -5873,6 +5872,8 @@ static void ext4_free_blocks_simple(struct inode *inode, ext4_fsblk_t block,
 	ext4_handle_dirty_metadata(NULL, NULL, gdp_bh);
 	sync_dirty_buffer(bitmap_bh);
 	sync_dirty_buffer(gdp_bh);
+
+err_out:
 	brelse(bitmap_bh);
 }