x86: clean up vdso_enabled type on x86_64

This fixes type of "vdso_enabled" on X86_64 to match extern in asm/elf.h.

Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/vdso/vma.c

@@ -16,7 +16,7 @@
 #include "vextern.h"		/* Just for VMAGIC.  */
 #undef VEXTERN
 
-int vdso_enabled = 1;
+unsigned int __read_mostly vdso_enabled = 1;
 
 extern char vdso_start[], vdso_end[];
 extern unsigned short vdso_sync_cpuid;