mfd: qcom_rpm: write fw_version to CTRL_REG

This is required as part of the initialization sequence on certain SoCs.

If these registers are not initialized, the hardware can be unresponsive.
This fixes the driver on apq8060 (HP TouchPad device).

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Signed-off-by: Lee Jones <lee.jones@linaro.org>