X86 ACPI: Use #ifdef not #if for CONFIG_X86 check

Fix a build warning on ia64:

include/linux/acpi.h:437:5: warning: "CONFIG_X86" is not defined

Signed-off-by: Tony Luck <tony.luck@intel.com>
Link: http://lkml.kernel.org/r/506f59ae9600b36a4@agluck-desktop.sc.intel.com


Cc: Len Brown <lenb@kernel.org>
Cc: Thomas Renninger <trenn@suse.de>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>