USB: pl2303: add support for RATOC REX-USB60F

pl2303: add support for RATOC REX-USB60F

This patch adds support for RATOC REX-USB60F Serial Adapters,
which is widely used in Japan recently.

Cc: stable <stable@kernel.org>
Signed-off-by: Akira Tsukamoto <akirat@rd.scei.sony.co.jp>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>