stable/btrfs: fix backport bug in d819d97e ("btrfs: honor path->skip_locking in backref code")

Upstream commit 38e3eebff643 ("btrfs: honor path->skip_locking in
backref code") was incorrectly backported to 4.14.y . It misses removal
of two lines from original commit, what cause deadlock.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=203993


Reported-by: Olivier Mazouffre <olivier.mazouffre@ims-bordeaux.fr>
Fixes: d819d97e ("btrfs: honor path->skip_locking in backref code")
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>