drm/msm/dpu: fix clock scaling on non-sc7180 board

c33b7c03 ("drm/msm/dpu: add support for clk and bw scaling for
display") has added support for handling bandwidth voting in kms path in
addition to old mdss path. However this broke all other platforms since
_dpu_core_perf_crtc_update_bus() will now error out instead of properly
calculating bandwidth and core clocks. Fix
_dpu_core_perf_crtc_update_bus() to just skip bandwidth setting instead
of returning an error in case kms->num_paths == 0 (MDSS is used for
bandwidth management).

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Fixes: c33b7c03 ("drm/msm/dpu: add support for clk and bw scaling for display")
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>