USB: serial: qcserial.c: use module_usb_serial_driver

This converts the qcserial.c driver to use the module_usb_serial_driver() call
instead of having to have a module_init/module_exit function, saving a lot
of duplicated code.

CC: Steven Hardy <shardy@redhat.com>
CC: Thomas Tuttle <ttuttle@chromium.org>
CC: Paul Gortmaker <paul.gortmaker@windriver.com>
CC: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>