x86: use WARN_ONCE in workaround for mtrr mask

so could help catch attention about bug in bios about mtrr mask setting.

WARN_ONCE got into mainline already, lets use it.
Signed-off-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/cpu/mtrr/generic.c

@@ -401,12 +401,7 @@ static void generic_get_mtrr(unsigned int reg, unsigned long *base,
 		tmp |= ~((1<<(hi - 1)) - 1);
 
 		if (tmp != mask_lo) {
-			static int once = 1;
-
-			if (once) {
-				printk(KERN_INFO "mtrr: your BIOS has set up an incorrect mask, fixing it up.\n");
-				once = 0;
-			}
+			WARN_ONCE(1, KERN_INFO "mtrr: your BIOS has set up an incorrect mask, fixing it up.\n");
 			mask_lo = tmp;
 		}
 	}