soc: qcom: rpmh: Use __fill_rpmh_msg API during rpmh_write()

Use __fill_rpmh_msg API during rpmh_write(). This allows to
remove duplication of code in error checking, copying commands
and setting message state.

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Maulik Shah <mkshah@codeaurora.org>
Link: https://lore.kernel.org/r/1606379490-4052-1-git-send-email-mkshah@codeaurora.org


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>