mm/huge_memory.c: minor lock simplification in __khugepaged_exit

The lock is released first thing in all three branches.  Simplify this by
unconditionally releasing lock and remove else clause which was only there
to be sure lock was released.

Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Johannes Weiner <jweiner@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>