mmc: slot-gpio: Remove override_active_level on WP

The argument "override_active_level" made it possible to
enforce a specific polarity on the write-protect
GPIO line. All callers in the kernel pass "false" to this
call after I have converted all drivers to use GPIO machine
descriptors, so remove the argument and clean out this.

This kind of polarity inversion should be handled by the
GPIO descriptor inside the GPIO library if needed.

This rids us of one instance of the kludgy calls into
the gpiod_get_raw_value() API.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>