drm/msm/dsi: Get rid of msm_dsi_config::num_dsi

drm/msm/dsi: Get rid of msm_dsi_config::num_dsi

In preparation for supporting multiple sets of possible base registers,
remove the num_dsi variable. We're comparing the io_start array contents
with the reg value from the DTS, so it will either match one of the
expected values or don't match against a zero (which we get from partial
array initialization).

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Signed-off-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/527658/
Link: https://lore.kernel.org/r/20230307-topic-dsi_qcm-v6-2-70e13b1214fa@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>