The current IDE Power Management code I wrote has a race on wakeup when
the master device got resumed, it may take a request.  At this point, a
PM resume request to a slave device of the same hwgroup would clear
hwgroup->rq and cause an Oops when the master device request completes. 

This patch fixes it.  Due to the context in which PM resume requests are
sent, just not clearing hwgroup->rq for these is enough. 

I also removed a useless debug message in the PM code that was
actually misleading (people though it indicated a problem while it
didn't, it's really useless) and fix a typo in a comment.