userns: Modify dqget to take struct kqid

Modify dqget to take struct kqid instead of a type and an identifier
pair.

Modify the callers of dqget in ocfs2 and dquot to take generate
a struct kqid so they can continue to call dqget.  The conversion
to create struct kqid should all be the final conversions that
are needed in those code paths.

Cc: Jan Kara <jack@suse.cz>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>