soc: qcom: rpmhpd: Provide some missing struct member descriptions

soc: qcom: rpmhpd: Provide some missing struct member descriptions

Fixes the following W=1 kernel build warning(s):

 drivers/soc/qcom/rpmhpd.c:52: warning: Function parameter or member 'parent' not described in 'rpmhpd'
 drivers/soc/qcom/rpmhpd.c:52: warning: Function parameter or member 'corner' not described in 'rpmhpd'
 drivers/soc/qcom/rpmhpd.c:52: warning: Function parameter or member 'active_corner' not described in 'rpmhpd'

Cc: Andy Gross <agross@kernel.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: linux-arm-msm@vger.kernel.org
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201103152838.1290217-22-lee.jones@linaro.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>