serial: 8250_dw: Fix the stub for dw8250_probe_acpi()

This fixes the stub for dw8250_probe_acpi() that is used
when compiling without ACPI enabled. The argument type was
wrong.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>