x86, apic: Use PAGE_SIZE instead of numbers

The whole page is reserved for IO-APIC fixmap
due to non-cacheable requirement. So lets note
this explicitly instead of playing with numbers.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: Maciej W. Rozycki <macro@linux-mips.org>
LKML-Reference: <20091108155356.GB25940@lenovo>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/apic/io_apic.c

@@ -4111,7 +4111,7 @@ void __init ioapic_init_mappings(void)
 		idx++;
 
 		ioapic_res->start = ioapic_phys;
-		ioapic_res->end = ioapic_phys + (4 * 1024) - 1;
+		ioapic_res->end = ioapic_phys + PAGE_SIZE-1;
 		ioapic_res++;
 	}
 }