btrfs: qgroup: Return actually freed bytes for qgroup release or free data

btrfs_qgroup_release/free_data() only returns 0 or a negative error
number (ENOMEM is the only possible error).

This is normally good enough, but sometimes we need the exact byte
count it freed/released.

Change it to return actually released/freed bytenr number instead of 0
for success.
And slightly modify related extent_changeset structure, since in btrfs
one no-hole data extent won't be larger than 128M, so "unsigned int"
is large enough for the use case.
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -4347,7 +4347,7 @@ int btrfs_check_data_free_space(struct inode *inode, u64 start, u64 len)
 
 	/* Use new btrfs_qgroup_reserve_data to reserve precious data space. */
 	ret = btrfs_qgroup_reserve_data(inode, start, len);
-	if (ret)
+	if (ret < 0)
 		btrfs_free_reserved_data_space_noquota(inode, start, len);
 	return ret;
 }

fs/btrfs/extent_io.h

@@ -209,7 +209,7 @@ struct extent_buffer {
  */
 struct extent_changeset {
 	/* How many bytes are set/cleared in this operation */
-	u64 bytes_changed;
+	unsigned int bytes_changed;
 
 	/* Changed ranges */
 	struct ulist range_changed;

fs/btrfs/qgroup.c

@@ -2897,6 +2897,7 @@ static int __btrfs_qgroup_release_data(struct inode *inode, u64 start, u64 len,
 		btrfs_qgroup_free_refroot(BTRFS_I(inode)->root->fs_info,
 				BTRFS_I(inode)->root->objectid,
 				changeset.bytes_changed);
+	ret = changeset.bytes_changed;
 out:
 	ulist_release(&changeset.range_changed);
 	return ret;