pwm: pca9685: Disable unused alternative addresses

The PCA9685 supports listening to 1 or more alternative I2C chip addresses
for some special features that this driver does not support.
By default the LED ALLCALL address is active (default 0x70), which causes
this chip to respond to address 0x70 in addition to its main address
(0x41). This is not desireable if there is another device on the same bus
that uses this address (like a TMP103 for example).
Since this feature is not supported by this driver, it is best to disable
these addresses in the chip to avoid unsuspected bus collisions.

Signed-off-by: David Jander <david@protonic.nl>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>