Btrfs: use set_nlink if our i_nlink is 0

Btrfs: use set_nlink if our i_nlink is 0

commit 9bf7a4890518186238d2579be16ecc5190a707c0 upstream.

We need to inc the nlink of deleted entries when running replay so we can do the
unlink on the fs_root and get everything cleaned up and then have the orphan
cleanup do the right thing.  The problem is inc_nlink complains about this, even
thought it still does the right thing.  So use set_nlink() if our i_nlink is 0
to keep users from seeing the warnings during log replay.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>