baycom_ser_fdx: also allow i/o ports >= 0x1000 and enhanced failure logging

The baycom_ser_fdx driver did not allow i/o ports >= 0x1000.  Now that
there are pci cards (with rs232 ports) which use for example 0xb800 this
limit should not exists.

Also, for non kernel coders find the cause of problems was challenging so I
added extra logging.

Signed-off-by: Folkert van Heusden <folkert@vanheusden.com>
Cc: Jeff Garzik <jeff@garzik.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>