USB: serial: fix hang when opening port

USB: serial: fix hang when opening port

commit eba0e3c3a0ba7b96f01cbe997680f6a4401a0bfc upstream.

Johan's 'fix use-after-free in TIOCMIWAIT' patchset[1] introduces
one bug which can cause kernel hang when opening port.

This patch initialized the 'port->delta_msr_wait' waitqueue head
to fix the bug which is introduced in 3.9-rc4.

[1], http://marc.info/?l=linux-usb&m=136368139627876&w=2

Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Acked-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>