clk: qcom: cpu-8996: use constant mask for pmux

Both pmux instances share the same width and shift. Specify the mask at
compile time to simplify functions.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20220714100351.1834711-7-dmitry.baryshkov@linaro.org