pinctrl: mediatek: paris: Fix pingroup pin config state readback

mtk_pconf_group_get(), used to read back pingroup pin config state,
simply returns a set of configs saved from a previous invocation of
mtk_pconf_group_set(). This is an unfiltered, unvalidated set passed
in from the pinconf core, which does not match the current hardware
state.

Since the driver library is designed to have one pin per group, pass
through mtk_pconf_group_get() to mtk_pinconf_get(), to read back the
current pin config state of the only pin in the group.

Also drop the assignment of pin config state to the group.

Fixes: 80525098

 ("pinctrl: mediatek: add pinctrl-paris that implements the vendor dt-bindings")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220308100956.2750295-5-wenst@chromium.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>