drm/amd/display: use a more accurate check in dm_helpers_dp_read_dpcd()

We should be checking if drm_dp_dpcd_read() returns the size that we are
asking it to read instead of just checking if it is greater than zero.
So, compare the return value of drm_dp_dpcd_read() to the requested
read size.
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_helpers.c

@@ -511,8 +511,8 @@ bool dm_helpers_dp_read_dpcd(
 		return false;
 	}
 
-	return drm_dp_dpcd_read(&aconnector->dm_dp_aux.aux, address,
-			data, size) > 0;
+	return drm_dp_dpcd_read(&aconnector->dm_dp_aux.aux, address, data,
+				size) == size;
 }
 
 bool dm_helpers_dp_write_dpcd(