x86: head_64.S - use IDT_ENTRIES instead of hardcoded number

Impact: cleanup
Signed-off-by: NCyrill Gorcunov <gorcunov@openvz.org>
Cc: heukelum@fastmail.fm
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/head_64.S

@@ -417,7 +417,7 @@ ENTRY(phys_base)
 	.section .bss, "aw", @nobits
 	.align L1_CACHE_BYTES
 ENTRY(idt_table)
-	.skip 256 * 16
+	.skip IDT_ENTRIES * 16
 
 	.section .bss.page_aligned, "aw", @nobits
 	.align PAGE_SIZE