[PATCH for 3.2] proc: Do not overflow get_{idle,iowait}_time for nohz

[Michal Hocko]

Hi Andrew, Thomas,
this is a regression fix (reported https://lkml.org/lkml/2011/11/24/102)
introduced by an earlier patch merged in 3.2-rc4.
I am not sure what is the correct channel so I am adding both of you. 
The original nohz /proc/stat fixlet was picked by Andrew and later
merged by Thomas IIRC.

Thanks!

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