serial: Make uart_port's ioport "unsigned long".

Otherwise the top 32-bits of the resource value get chopped
off on 64-bit systems, and the resulting I/O accesses go to
random places.

Thanks to testing and debugging by Josip Rodin, which helped
track this down.

Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>