amdgpu: fix NULL pointer dereference at tonga_check_states_equal

The event_data passed from pem_fini was not cleared upon initialization.
This caused NULL checks to pass and cast_const_phw_tonga_power_state to
attempt to dereference an invalid pointer. Clear the event_data in
pem_init and pem_fini before calling pem_handle_event.

Reviewed-by:  Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Bradley Pankow <btpankow@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/powerplay/eventmgr/eventmgr.c

@@ -31,7 +31,7 @@
 static int pem_init(struct pp_eventmgr *eventmgr)
 {
 	int result = 0;
-	struct pem_event_data event_data;
+	struct pem_event_data event_data = { {0} };
 
 	/* Initialize PowerPlay feature info */
 	pem_init_feature_info(eventmgr);
@@ -52,7 +52,7 @@ static int pem_init(struct pp_eventmgr *eventmgr)
 
 static void pem_fini(struct pp_eventmgr *eventmgr)
 {
-	struct pem_event_data event_data;
+	struct pem_event_data event_data = { {0} };
 
 	pem_uninit_featureInfo(eventmgr);
 	pem_unregister_interrupts(eventmgr);