drm/amd/display: Fix typo when retrieving dppclk from UEFI config

[why]
In some boot configurations we need to retrieve the currently
UEFI-set dppclk, but there was a typo in the calculation

[how]
Fix typo to make dpp_clk calculate off dpp_clk divider instead of
disp_clk
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Martin Leung <martin.leung@amd.com>
Reviewed-by: Sung Lee <Sung.Lee@amd.com>
Acked-by: Eryk Brol <eryk.brol@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/clk_mgr/dcn20/dcn20_clk_mgr.c

@@ -361,7 +361,7 @@ void dcn2_read_clocks_from_hw_dentist(struct clk_mgr *clk_mgr_base)
 	REG_GET(DENTIST_DISPCLK_CNTL, DENTIST_DPPCLK_WDIVIDER, &dppclk_wdivider);
 
 	disp_divider = dentist_get_divider_from_did(dispclk_wdivider);
-	dpp_divider = dentist_get_divider_from_did(dispclk_wdivider);
+	dpp_divider = dentist_get_divider_from_did(dppclk_wdivider);
 
 	if (disp_divider && dpp_divider) {
 		/* Calculate the current DFS clock, in kHz.*/