drm/amd/display/dc/dce/dce_aux: Mark 'dce_aux_transfer_raw' as __maybe_unused

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/../display/dc/dce/dce_aux.c: In function ‘dce_aux_transfer_raw’:
 drivers/gpu/drm/amd/amdgpu/../display/dc/dce/dce_aux.c:579:7: warning: variable ‘bytes_replied’ set but not used [-Wunused-but-set-variable]

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -576,7 +576,7 @@ int dce_aux_transfer_raw(struct ddc_service *ddc,
 	*operation_result = get_channel_status(aux_engine, &returned_bytes);
 
 	if (*operation_result == AUX_CHANNEL_OPERATION_SUCCEEDED) {
-		int bytes_replied = 0;
+		int __maybe_unused bytes_replied = 0;
 		bytes_replied = read_channel_reply(aux_engine, payload->length,
 					 payload->data, payload->reply,
 					 &status);