drm/amd/display: Do not return negative stream id for array

[WHY]
resource_stream_to_stream_idx returns an array index and it return -1
when not found; however, -1 is not a valid array index number.

[HOW]
When this happens, call ASSERT(), and return a zero instead.

This fixes an OVERRUN and an NEGATIVE_RETURNS issues reported by Coverity.

Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: Alex Hung

drivers/gpu/drm/amd/display/dc/core/dc_resource.c

@@ -2243,6 +2243,13 @@ static int resource_stream_to_stream_idx(struct dc_state *state,
 			stream_idx = i;
 			break;
 		}
+
+	/* never return negative array index */
+	if (stream_idx == -1) {
+		ASSERT(0);
+		return 0;
+	}
+
 	return stream_idx;
 }