serial: add PNP ID GVC0303 for Archtek 3334BRV ISA modem

Thomas Lehmann <thomas.lehmann@alumni.tu-berlin.de> verified that this
entry works.

Signed-off-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>