ampton: Check return value in board specific mux init
ampton: Check return value in board specific mux init

This patch adds checking if I2C writes to PS8751 muxer succeded.
There are many reasons causing fail during mux_write(), one of them
is that device is in standby mode. With this CL, problems will be
reported to developer.

BUG=b:151155658
BRANCH=none
TEST=make -j buildall

Signed-off-by: Patryk Duda <6aed17a362577cf10cb5675888c1635d522769c1@semihalf.com>
Change-Id: Ide342ed8c713e58d91880d41a584c56866f95fec
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2633982
Reviewed-by: Aseda Aboagye <12c9b286316a940fd31c24070da5ab64cdd4d0e7@chromium.org>
Reviewed-by: Diana Z <cb2016afc7183e5356c690dc63b4ba817470501a@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec