btrfs: simplify logic to decrement snapshot counter at btrfs_mksnapshot()

There's no point in having a 'snapshot_force_cow' variable to track if we
need to decrement the root->snapshot_force_cow counter, as we never jump
to the 'out' label after incrementing the counter. Simplify this by
removing the variable and always decrementing the counter before the 'out'
label, right after the call to btrfs_mksubvol().

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

Author: fdmanana

fs/btrfs/ioctl.c

@@ -1049,7 +1049,6 @@ static noinline int btrfs_mksnapshot(const struct path *parent,
 				   struct btrfs_qgroup_inherit *inherit)
 {
 	int ret;
-	bool snapshot_force_cow = false;
 
 	/*
 	 * Force new buffered writes to reserve space even when NOCOW is
@@ -1068,15 +1067,13 @@ static noinline int btrfs_mksnapshot(const struct path *parent,
 	 * creation.
 	 */
 	atomic_inc(&root->snapshot_force_cow);
-	snapshot_force_cow = true;
 
 	btrfs_wait_ordered_extents(root, U64_MAX, NULL);
 
 	ret = btrfs_mksubvol(parent, idmap, name, namelen,
 			     root, readonly, inherit);
+	atomic_dec(&root->snapshot_force_cow);
 out:
-	if (snapshot_force_cow)
-		atomic_dec(&root->snapshot_force_cow);
 	btrfs_drew_read_unlock(&root->snapshot_lock);
 	return ret;
 }