sched: Clean up some typos and grammatical errors in code/comments

Signed-off-by: Zhihui Zhang <zzhsuny@gmail.com>
Cc: peterz@infradead.org
Link: http://lkml.kernel.org/r/1411262676-19928-1-git-send-email-zzhsuny@gmail.com


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