gpioiic: never drive lines active high

I2C communication is done by a combination of driving a line low or
letting it float, so that it is either pulled up or driven low by
another party.

r355276 besides the stated goal of the change -- using the new GPIO API

• also changed the logic, so that active state is signaled by actively

driving a line.

That worked with iicbb prior to r362042, but stopped working after that
commit on at least some hardware. My guess that the breakage was
related to getting an ACK bit. A device expected to be able to drive
SDA actively low, but controller was actively driving it high for some
time.

Anyway, this change seems to fix the problem.
Tested using gpioiic on Orange Pi PC Plus with HTU21 sensor.

Reported by: Nick Kostirya <nikolay.kostirya@i11.co>
Reviewed by: manu
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D25684