x86: cpufeature.h fix name for X86_FEATURE_MCE

X86_FEATURE_MCE = Machine Check Exception
X86_FEATURE_MCA = Machine Check Architecture

[ Impact: cleanup ]

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
LKML-Reference: <1241329295.6321.1.camel@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>