x86, mce: Rename sysfs variables

Shorten variable names. This also compacts the code a bit.

	device_mce		=> mce_dev
	mce_device_initialized	=> mce_dev_initialized
	mce_attribute		=> mce_attrs

[ Impact: cleanup ]

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>