x86, mce: Fix mce printing

This patch:

 - Adds print_mce_head() instead of first flag
 - Makes the header to be printed always
 - Stops double printing of corrected errors

[ This portion originates from Huang Ying's patch ]

Originally-From: Huang Ying <ying.huang@intel.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
LKML-Reference: <4A30AC83.5010708@jp.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>