Impact: cleanup, fix

Clean up sys_shutdown() exit path.  Factor out common code.  Return
correct error code instead of always 0 on failure.
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>