x86, mce: fix "mce" boot option handling for CONFIG_X86_NEW_MCE

"mce argument mce ignored. Please use /sys" message shouldn't
be printed when using "mce" boot option.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Reviewed-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>