iio: potentiometer: tpl0102: remove unneeded i2c check functionality test

Actually I2C_FUNC_SMBUS_WORD_DATA isn't need for this device, and regmap
handles all single byte reads transparently.

Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>