drm/amd/display: Spinlock before reading event

[WHY & HOW]
A read of acrtc_attach->base.state->event was not locked so moving it
inside the spinlock.

This fixes a LOCK_EVASION issue reported by Coverity.
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -8806,15 +8806,13 @@ static void amdgpu_dm_commit_planes(struct drm_atomic_state *state,
 				bundle->stream_update.vrr_infopacket =
 					&acrtc_state->stream->vrr_infopacket;
 		}
-	} else if (cursor_update && acrtc_state->active_planes > 0 &&
-		   acrtc_attach->base.state->event) {
-		drm_crtc_vblank_get(pcrtc);
-
+	} else if (cursor_update && acrtc_state->active_planes > 0) {
 		spin_lock_irqsave(&pcrtc->dev->event_lock, flags);
-
-		acrtc_attach->event = acrtc_attach->base.state->event;
-		acrtc_attach->base.state->event = NULL;
-
+		if (acrtc_attach->base.state->event) {
+			drm_crtc_vblank_get(pcrtc);
+			acrtc_attach->event = acrtc_attach->base.state->event;
+			acrtc_attach->base.state->event = NULL;
+		}
 		spin_unlock_irqrestore(&pcrtc->dev->event_lock, flags);
 	}