x86, mce: Cleanup param parser

- Fix the comment formatting.

- The error path does not return 0, and printk lacks level and "\n".

- Move __setup("nomce") next to mcheck_disable().

- Improve readability etc.

[ Impact: cleanup ]

Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Acked-by: Andi Kleen <ak@linux.intel.com>
LKML-Reference: <49CB3F38.7090703@jp.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>