drm/amd/display: remove set but not used variable 'speakers' in dce_stream_encoder.c

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/amd/display/dc/dce/dce_stream_encoder.c:1339:11: warning: variable ‘speakers’ set but not used [-Wunused-but-set-variable]

It is introduced by commit 4562236b ("drm/amd/dc:
Add dc display driver (v2)"), but never used, so remove it.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/dce/dce_stream_encoder.c

@@ -1336,7 +1336,6 @@ static void dce110_se_audio_setup(
 {
 	struct dce110_stream_encoder *enc110 = DCE110STRENC_FROM_STRENC(enc);
 
-	uint32_t speakers = 0;
 	uint32_t channels = 0;
 
 	ASSERT(audio_info);
@@ -1344,7 +1343,6 @@ static void dce110_se_audio_setup(
 		/* This should not happen.it does so we don't get BSOD*/
 		return;
 
-	speakers = audio_info->flags.info.ALLSPEAKERS;
 	channels = speakers_to_channels(audio_info->flags.speaker_flags).all;
 
 	/* setup the audio stream source select (audio -> dig mapping) */