sched: Fix typo in struct sched_avg member description

Remove extra 'for' from the description about member of
struct sched_avg.

Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Cc: pjt@google.com
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/20130627060409.GB18582@linux.vnet.ibm.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>