tty/8250_pnp: serial port detection regression since v3.7

The InsydeH2O BIOS (version dated 09/12/2011) has the following in
its pnp resouces for its serial ports:

$ cat /sys/bus/pnp/devices/00:0b/resources
state = active
io disabled
irq disabled

We do not check if the resources are disabled, and create a bogus
ttyS* device. Since commit 835d844d (8250_pnp: do pnp probe
before legacy probe) we get a bogus ttyS0, which prevents the legacy
probe from detecting it.

Note, the BIOS can also be upgraded, fixing this problem, but for people
who can't do that, this fix is needed.

Reported-by: Vincent Deffontaines <vincent@gryzor.com>
Tested-by: Vincent Deffontaines <vincent@gryzor.com>
Signed-off-by: Sean Young <sean@mess.org>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>