USB: serial: ir-usb: add missing endpoint sanity check

Add missing endpoint sanity check to avoid dereferencing a NULL-pointer
on open() in case a device lacks a bulk-out endpoint.

Note that prior to commit f4a4cbb2 ("USB: ir-usb: reimplement using
generic framework") the oops would instead happen on open() if the
device lacked a bulk-in endpoint and on write() if it lacked a bulk-out
endpoint.

Fixes: f4a4cbb2 ("USB: ir-usb: reimplement using generic framework")
Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Johan Hovold <johan@kernel.org>