In the case of ((max9877_regs[reg] >> shift) & mask) != val
but ((max9877_regs[reg2] >> shift) & mask) == val2,
current code does not update the registers.

Fix the logic to update registers if either val or val2 is changed.
Signed-off-by: NAxel Lin <axel.lin@gmail.com>
Signed-off-by: NMark Brown <broonie@opensource.wolfsonmicro.com>