i2c: omap: switch to new generic helper for getting selected mux-state

i2c: omap: switch to new generic helper for getting selected mux-state

Multiplexer subsystem has added generic helper functions for getting an
already selected mux-state object.

Replace existing logic in probe with the equivalent helper function.

There is a functional difference in that the mux is now automatically
deselected on release, replacing the explicit mux_state_deselect call.

This change is only compile-tested.

Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Andreas Kemnade <andreas@kemnade.info>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Josua Mayer <josua@solid-run.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>