x86, mce: drop BKL in mce_open

BKL is not needed for anything in mce_open because it has
an own spinlock. Remove it.

[ Impact: cleanup ]

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>