convert btrfs to ->evict_inode()

NB: do we want btrfs_wait_ordered_range() on eviction of
inodes with positive i_nlink on subvolume with zero root_refs?
If not, btrfs_evict_inode() can be simplified by unconditionally
bailing out in case of i_nlink > 0 in the very beginning...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index f2393b3..1776dbd 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -797,7 +797,7 @@
 
 static const struct super_operations btrfs_super_ops = {
 	.drop_inode	= btrfs_drop_inode,
-	.delete_inode	= btrfs_delete_inode,
+	.evict_inode	= btrfs_evict_inode,
 	.put_super	= btrfs_put_super,
 	.sync_fs	= btrfs_sync_fs,
 	.show_options	= btrfs_show_options,