msm: clk: qcom: power on PLL when reading PLL registers

On sm8150 platform, reading register of DSI PLL would
fail if PLL is not powered up, so enable DSI PLL power
before reading operation.

CRs-Fixed: 2225631
Change-Id: I2d589ee39b95234b06c8ad6556725f94deea2c10
Signed-off-by: Ray Zhang <rayz@codeaurora.org>
Signed-off-by: Yujun Zhang <yujunzhang@codeaurora.org>