ARM: fix missing branch in __error_a

ARM: fix missing branch in __error_a

When DEBUG_LL is not set, we don't want __error_a re-entering
__lookup_machine_type - we want it to go to the error function.  This
used to be the case before we reorganized the layout for hotplug cpu,
as we used to fall through to __error.  With the changed layout, we
need an explicit branch here instead.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>