x86: Fix typo preventing msr_set/clear_bit from having an effect

Due to a typo the msr accessor function introduced in
22085a66 didn't have any lasting
effects because they accidentally wrote the old value back.

After c0a639ad

 this at the very least
this causes cpuid limits not to be lifted on some cpus leading to
missing capabilities for those.

Signed-off-by: Andres Freund <andres@anarazel.de>
Link: http://lkml.kernel.org/r/1399598957-7011-2-git-send-email-andres@anarazel.de
Cc: Borislav Petkov <bp@suse.de>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>