autofs4: use struct qstr in waitq.c

The autofs_wait_queue already contains all of the fields of the
struct qstr, so change it into a qstr.

This patch, from Jeff Moyer, has been modified a liitle by myself.

Signed-off-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Ian Kent <raven@themaw.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>