Add I2C-ack handling code to kerkey_write_i2c().
Add I2C-ack handling code to kerkey_write_i2c().

Testing showed, that the device sometimes NACKs when attempting
to write to it. Let's retry a couple of times, like we do in
kerkey_read_i2c().

Signed-off-by: Christoph Müllner <a5d225a1160170157d2efb6ceb19cc9ac620c91b@gmail.com>

cmuellner/libifdkerkey