drm/amd/display: Update number of dcn21 audio endpoints

[WHY]
Number of audio endpoints wasn't updated from dcn20's 6 when created

[HOW]
Changed num_audio to 4 to match the correct sbios value
Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Reviewed-by: Yongqiang Sun <yongqiang.sun@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dcn21/dcn21_resource.c

@@ -726,7 +726,7 @@ static const struct resource_caps res_cap_rn = {
 		.num_timing_generator = 4,
 		.num_opp = 4,
 		.num_video_plane = 4,
-		.num_audio = 6, // 6 audio endpoints.  4 audio streams
+		.num_audio = 4, // 4 audio endpoints.  4 audio streams
 		.num_stream_encoder = 5,
 		.num_pll = 5,  // maybe 3 because the last two used for USB-c
 		.num_dwb = 1,