gfs2: remove redundant check in gfs2_rgrp_go_lock

Before this patch, function gfs2_rgrp_go_lock checked if GL_SKIP and
ar_rgrplvb were both true. However, GL_SKIP is only set for rgrps if
ar_rgrplvb is true (see gfs2_inplace_reserve). This patch simply removes
the redundant check.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>