drm/msm/dpu: remove extra clk_round_rate() call

The dev_pm_opp_set_rate() already contains a call for clk_round_rate for
the passed value. Stop calling it manually from
_dpu_core_perf_get_core_clk_rate(). It is slightly incorrect to call it
this way, as we should round the final calculated clock rate rather than
rounding all the intermediate values.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/550212/
Link: https://lore.kernel.org/r/20230730010102.350713-9-dmitry.baryshkov@linaro.org