pinctrl: meson: fix pull enable register calculation

We just changed the code so we apply bias disable on the correct
register but forgot to align the register calculation. The result
is that we apply the change on the correct register, but possibly
at the incorrect offset/bit

This went undetected because offsets tends to be the same between
REG_PULL and REG_PULLEN for a given pin the EE controller. This
is not true for the AO controller.

Fixes: e39f9dd8 ("pinctrl: meson: fix pinconf bias disable")
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>