drm/amd/display: Avoid reading audio pattern past AUDIO_CHANNELS_COUNT

A faulty receiver might report an erroneous channel count. We
should guard against reading beyond AUDIO_CHANNELS_COUNT as
that would overflow the dpcd_pattern_period array.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org

Author: Harry Wentland

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

@@ -4440,7 +4440,7 @@ static void dp_test_get_audio_test_data(struct dc_link *link, bool disable_video
 		&dpcd_pattern_type.value,
 		sizeof(dpcd_pattern_type));
 
-	channel_count = dpcd_test_mode.bits.channel_count + 1;
+	channel_count = min(dpcd_test_mode.bits.channel_count + 1, AUDIO_CHANNELS_COUNT);
 
 	// read pattern periods for requested channels when sawTooth pattern is requested
 	if (dpcd_pattern_type.value == AUDIO_TEST_PATTERN_SAWTOOTH ||