pch_uart: Set PCIe bus number using probe parameter

Currently, PCIe bus number is set as fixed value "2".
However, PCIe bus number is not always "2".
This patch sets bus number using probe() parameter.

Signed-off-by: Tomoya MORINAGA <tomoya-linux@dsn.okisemi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>