drm/amd/display: Check returned status from core_link_read_dpcd

[WHAT]
The function core_link_read_dpcd returns status which is not used at
all, making them useless assignments.

[HOW]
Print error messages if core_link_read_dpcd does not return DC_OK.

This fixes 2 UNUSED_VALUE issues reported by Coverity.

Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/link/protocols/link_dp_capability.c

@@ -1854,6 +1854,9 @@ static bool retrieve_link_cap(struct dc_link *link)
 				DP_FEC_CAPABILITY,
 				&link->dpcd_caps.fec_cap.raw,
 				sizeof(link->dpcd_caps.fec_cap.raw));
+		if (status != DC_OK)
+			DC_LOG_ERROR("%s:%d: core_link_read_dpcd (DP_FEC_CAPABILITY) failed\n", __func__, __LINE__);
+
 		status = core_link_read_dpcd(
 				link,
 				DP_DSC_SUPPORT,
@@ -1876,6 +1879,9 @@ static bool retrieve_link_cap(struct dc_link *link)
 					DP_DSC_BRANCH_OVERALL_THROUGHPUT_0,
 					link->dpcd_caps.dsc_caps.dsc_branch_decoder_caps.raw,
 					sizeof(link->dpcd_caps.dsc_caps.dsc_branch_decoder_caps.raw));
+			if (status != DC_OK)
+				DC_LOG_ERROR("%s:%d: core_link_read_dpcd (DP_DSC_BRANCH_OVERALL_THROUGHPUT_0) failed\n", __func__, __LINE__);
+
 			DC_LOG_DSC("DSC branch decoder capability is read at link %d", link->link_index);
 			DC_LOG_DSC("\tBRANCH_OVERALL_THROUGHPUT_0 = 0x%02x",
 					link->dpcd_caps.dsc_caps.dsc_branch_decoder_caps.fields.BRANCH_OVERALL_THROUGHPUT_0);