drm/nv50-/disp: handle supervisor tasks from workqueue

i2c_algo_bit sleeps...

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
diff --git a/drivers/gpu/drm/nouveau/nv50_display.c b/drivers/gpu/drm/nouveau/nv50_display.c
index 75d1161..2cd3797 100644
--- a/drivers/gpu/drm/nouveau/nv50_display.c
+++ b/drivers/gpu/drm/nouveau/nv50_display.c
@@ -424,7 +424,10 @@
 static bool
 evo_sync_wait(void *data)
 {
-	return nouveau_bo_rd32(data, EVO_MAST_NTFY) != 0x00000000;
+	if (nouveau_bo_rd32(data, EVO_MAST_NTFY) != 0x00000000)
+		return true;
+	usleep_range(1, 2);
+	return false;
 }
 
 static int