USB-serial: pl2303: use 1.5 instead of 2 stop bits with 5 data bits

This is how "real" UARTs (e.g. 16550) work and AFAIK what RS232 specifies, too.
Make the driver more compliant.

Signed-off-by: Frank Schaefer <schaefer.frank@gmx.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>