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>

arch/arm/kernel/head-common.S

@@ -60,6 +60,8 @@ str_a1:	.asciz	"\nError: unrecognized/unsupported machine ID (r1 = 0x"
 str_a2:	.asciz	").\n\nAvailable machine support:\n\nID (hex)\tNAME\n"
 str_a3:	.asciz	"\nPlease check your kernel config and/or bootloader.\n"
 	.align
+#else
+	b	__error
 #endif
 
 /*