pl2303: improve the chip type information output on startup

The chip type distinction is getting more and more relevant and
complicating, so always print the chip type.
Printing a name string is also much better than just printing an
internal index number.

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>