drm/amd/display: Fix divide-by-zero in DPPCLK and DISPCLK calculation

[Why]
Certain use cases will pass in zero in the new_clocks parameter for all
clocks. This results in a divide-by-zero error when attempting to round
up the new clock.

When new_clocks are zero, no rounding is required, so we can skip it.

[How]
Guard the division calculation with a check to make sure clocks are not
zero.
Tested-by: NDaniel Wheeler <daniel.wheeler@amd.com>
Acked-by: NRodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: NGeorge Shen <george.shen@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/clk_mgr/dcn32/dcn32_clk_mgr.c

@@ -335,14 +335,16 @@ static void dcn32_update_dppclk_dispclk_freq(struct clk_mgr_internal *clk_mgr, s
 	int dpp_divider = 0;
 	int disp_divider = 0;
 
-	dpp_divider = DENTIST_DIVIDER_RANGE_SCALE_FACTOR
-			* clk_mgr->base.dentist_vco_freq_khz / new_clocks->dppclk_khz;
-	disp_divider = DENTIST_DIVIDER_RANGE_SCALE_FACTOR
-			* clk_mgr->base.dentist_vco_freq_khz / new_clocks->dispclk_khz;
-
-	// Divide back the previous result to round up to the actual clock value that will be set from divider
-	new_clocks->dppclk_khz = (DENTIST_DIVIDER_RANGE_SCALE_FACTOR * clk_mgr->base.dentist_vco_freq_khz) / dpp_divider;
-	new_clocks->dispclk_khz = (DENTIST_DIVIDER_RANGE_SCALE_FACTOR * clk_mgr->base.dentist_vco_freq_khz) / disp_divider;
+	if (new_clocks->dppclk_khz) {
+		dpp_divider = DENTIST_DIVIDER_RANGE_SCALE_FACTOR
+				* clk_mgr->base.dentist_vco_freq_khz / new_clocks->dppclk_khz;
+		new_clocks->dppclk_khz = (DENTIST_DIVIDER_RANGE_SCALE_FACTOR * clk_mgr->base.dentist_vco_freq_khz) / dpp_divider;
+	}
+	if (new_clocks->dispclk_khz > 0) {
+		disp_divider = DENTIST_DIVIDER_RANGE_SCALE_FACTOR
+				* clk_mgr->base.dentist_vco_freq_khz / new_clocks->dispclk_khz;
+		new_clocks->dispclk_khz = (DENTIST_DIVIDER_RANGE_SCALE_FACTOR * clk_mgr->base.dentist_vco_freq_khz) / disp_divider;
+	}
 }
 
 static void dcn32_update_clocks(struct clk_mgr *clk_mgr_base,