PCA9632 defaults to open-drain
PCA9633/4/5 defaults to totem-pole

the driver assumed that totem-pole default and didn't actively set
the value; the MODE2 register is now written if platform
data indicating the mode is given
Signed-off-by: NPeter Meerwald <pmeerw@pmeerw.net>
Signed-off-by: NBryan Wu <cooloney@gmail.com>