USB: serial: make use of UART_LCR_WLEN() + tty_get_char_size()

Having a generic UART_LCR_WLEN() macro and the tty_get_char_size()
helper, we can remove all those repeated switch-cases in drivers.

Cc: Johan Hovold <johan@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220224095558.30929-3-jslaby@suse.cz


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>