power: bq24735-charger: fix failed i2c with ac-detect

When an ac-detect pin exists, but the charger is not plugged in,
the chip will not respond to i2c messages, causing the module to
fail when inserted.

Signed-off-by: Jonathan Tinkham <sctincman@gmail.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>