pinctrl: meson: Fix wrong shift value when get drive-strength

pinctrl: meson: Fix wrong shift value when get drive-strength

In meson_pinconf_get_drive_strength, variable bit is calculated by
meson_calc_reg_and_bit, this value is the offset from the first pin of a
certain bank to current pin, while Meson SoCs use two bits for each pin
to depict drive-strength. So a left shift by 1 should be done or node
pinconf-pins shows wrong message.

Fixes: 6ea3e3bbef37 ("pinctrl: meson: add support of drive-strength-microamp")

Signed-off-by: Qianggui Song <qianggui.song@amlogic.com>
Link: https://lore.kernel.org/r/20191226023734.9631-1-qianggui.song@amlogic.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>