sched/fair: Update comments after a variable rename

sched/fair: Update comments after a variable rename

The following commit:

  ed82b8a1ff76 ("sched/core: Move the sched_to_prio[] arrays out of line")

renamed prio_to_weight to sched_prio_to_weight, but the old name was not
updated in comments.

Signed-off-by: Yuyang Du <yuyang.du@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1459292871-22531-1-git-send-email-yuyang.du@intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>