btrfs: cleanup helpers that reset balance state

The function __cancel_balance name is confusing with the cancel
operation of balance and it really resets the state of balance back to
zero. The unset_balance_control helper is called only from one place and
simple enough to be inlined.

Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index f0d0aef..6c759f2 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4459,10 +4459,10 @@ static long btrfs_ioctl_balance(struct file *file, void __user *arg)
 
 do_balance:
 	/*
-	 * Ownership of bctl and filesystem flag BTRFS_FS_EXCL_OP
-	 * goes to to btrfs_balance.  bctl is freed in __cancel_balance,
-	 * or, if restriper was paused all the way until unmount, in
-	 * free_fs_info.  The flag should be cleared after __cancel_balance.
+	 * Ownership of bctl and filesystem flag BTRFS_FS_EXCL_OP goes to
+	 * btrfs_balance.  bctl is freed in reset_balance_state, or, if
+	 * restriper was paused all the way until unmount, in free_fs_info.
+	 * The flag should be cleared after reset_balance_state.
 	 */
 	need_unlock = false;