pty: Fix lock inversion

pty: Fix lock inversion

The ptmx_open path takes the tty and devpts locks in the wrong order
because tty_init_dev locks and returns a locked tty.  As far as I can
tell this is actually safe anyway because the tty being returned is new
so nobody can get a reference to lock it at this point.

However we don't even need the devpts lock at this point, it's only held
as a byproduct of the way the locks were pushe down.

Signed-off-by: Alan Cox <[email protected]>
Acked-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>