drm/amd/display: Avoid set zero in the requested clk

[Why]
Sometimes CRTCs can be disabled due to display unplugging or temporarily
transition in the userspace; in these circumstances, DCE tries to set
the minimum clock threshold. When we have this situation, the function
bw_calcs is invoked with number_of_displays set to zero, making DCE set
dispclk_khz and sclk_khz to zero. For these reasons, we have seen some
ATOM bios errors that look like:

[drm:atom_op_jump [amdgpu]] *ERROR* atombios stuck in loop for more than
5secs aborting
[drm:amdgpu_atom_execute_table_locked [amdgpu]] *ERROR* atombios stuck
executing EA8A (len 761, WS 0, PS 0) @ 0xEABA

[How]
This error happens due to an attempt to optimize the bandwidth using the
sclk, and the dispclk clock set to zero. Technically we handle this in
the function dce112_set_clock, but we are not considering the case that
this value is set to zero. This commit fixes this issue by ensuring that
we never set a minimum value below the minimum clock threshold.

Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@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/dce112/dce112_clk_mgr.c

@@ -79,8 +79,7 @@ int dce112_set_clock(struct clk_mgr *clk_mgr_base, int requested_clk_khz)
 	memset(&dce_clk_params, 0, sizeof(dce_clk_params));
 
 	/* Make sure requested clock isn't lower than minimum threshold*/
-	if (requested_clk_khz > 0)
-		requested_clk_khz = max(requested_clk_khz,
+	requested_clk_khz = max(requested_clk_khz,
 				clk_mgr_dce->base.dentist_vco_freq_khz / 62);
 
 	dce_clk_params.target_clock_frequency = requested_clk_khz;