ASoC: rk817: fix a warning in rk817_probe()

The return value of snd_soc_component_write() is stored but not
evaluated and this results in a warning when W=1 is set. Stop storing
the return value to be consistent with all other calls of
snd_soc_component_write() and to remove the warning.

Fixes: 0d6a04da ("ASoC: Add Rockchip rk817 audio CODEC support")

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>