gfs2: Fix error exit in do_xmote

Before this patch, if an error was detected from glock function go_sync
by function do_xmote, it would return.  But the function had temporarily
unlocked the gl_lockref spin_lock, and it never re-locked it.  When the
caller of do_xmote tried to unlock it again, it was already unlocked,
which resulted in a corrupted spin_lock value.

This patch makes sure the gl_lockref spin_lock is re-locked after it is
unlocked.

Thanks to Wu Bo <wubo40@huawei.com> for reporting this problem.

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