mfd: Staticise internal functions in HTC I2CCPLD driver

Most of these are GPIO operations, though a couple are just internal only
functions.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Cory Maccarrone <darkstar6262@gmail.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>