x86_64: arch/x86_64/kernel/aperture.c lower printk severity

Users that use kernel log filtering (e.g.  via syslogd or a proprietry method)
wouldn't like to see warning prints that are not really warnings.

Signed-off-by: Dan Aloni <da-x@monatomic.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>