clk: qcom: mmcc-msm8974: use ARRAY_SIZE instead of specifying num_parents

Use ARRAY_SIZE() instead of manually specifying num_parents. This makes
adding/removing entries to/from parent_data easy and errorproof.

Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221204124508.1415713-7-dmitry.baryshkov@linaro.org