i2c: mux: gpio: Replace custom acpi_get_local_address()

Recently ACPI gained the acpi_get_local_address() API which may be used
instead of home grown i2c_mux_gpio_get_acpi_adr().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Evan Green <evgreen@chromium.org>
Acked-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@kernel.org>