mfd: Push byte swaps out of wm8994 bulk read path

For consistency with the write path push byte swaps of the WM8994 register
data out of the bulk read data path into the per-register APIs. The only
user of the bulk register read is the interrupt code which is updated to
do the swaps itself part of this patch.

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