Simplify the code in cpuid_open

[John Kacur]

Peter picked up my patch for tip/x86/cpu that removes the bkl in 
cpuid_open. Ingo subsequently merged that into tip/master.

The following patch folds back-in tglx's patch that we should have known 
about if we had looked into tip/rt/bkl in the first place!

Please pick it up for tip/x86/cpu and tip/master.