USB: serial: pl2303 works at 500kbps

My PL2303HX works at 500kbps after applying this patch.
I suppose that it could work at other non standard speeds since this fix

"correctly handle baudrates above 115200"
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/usb/serial/pl2303.c?id=8d48fdf689fed2c73c493e5146d1463689246442

came after this one

"fix baud rate handling in case of unsupported values"
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/drivers/usb/serial/pl2303.c?id=25b8286805e856c8c7fda127018e31032c918015



but I only can test it with 500000.
Patch made against mainline but tested with 3.4.45

Signed-off-by: Luca Olivetti <luca@ventoso.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>