drm/radeon: initialize sadb to NULL in the audio code

Fixes kfree of the sadb buffer when it's NULL.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/dce3_1_afmt.c

@@ -32,7 +32,7 @@ static void dce3_2_afmt_write_speaker_allocation(struct drm_encoder *encoder)
 	struct drm_connector *connector;
 	struct radeon_connector *radeon_connector = NULL;
 	u32 tmp;
-	u8 *sadb;
+	u8 *sadb = NULL;
 	int sad_count;
 
 	list_for_each_entry(connector, &encoder->dev->mode_config.connector_list, head) {

drivers/gpu/drm/radeon/dce6_afmt.c

@@ -155,7 +155,7 @@ void dce6_afmt_write_speaker_allocation(struct drm_encoder *encoder)
 	struct drm_connector *connector;
 	struct radeon_connector *radeon_connector = NULL;
 	u32 offset, tmp;
-	u8 *sadb;
+	u8 *sadb = NULL;
 	int sad_count;
 
 	if (!dig || !dig->afmt || !dig->afmt->pin)

drivers/gpu/drm/radeon/evergreen_hdmi.c

@@ -133,7 +133,7 @@ static void dce4_afmt_write_speaker_allocation(struct drm_encoder *encoder)
 	struct drm_connector *connector;
 	struct radeon_connector *radeon_connector = NULL;
 	u32 tmp;
-	u8 *sadb;
+	u8 *sadb = NULL;
 	int sad_count;
 
 	list_for_each_entry(connector, &encoder->dev->mode_config.connector_list, head) {