Change framebuffer.clear to use background color

samples/stm32f746g-discovery/disco-light.dart

Index: samples/stm32f746g-discovery/disco-light.dart
diff --git a/samples/stm32f746g-discovery/disco-light.dart b/samples/stm32f746g-discovery/disco-light.dart
index e49f27d9b362bc461aaf1778b9c2d48ca47d9a81..2081efc471d964bdb23b3890b7cf5b8c71734b2e 100644
--- a/samples/stm32f746g-discovery/disco-light.dart
+++ b/samples/stm32f746g-discovery/disco-light.dart
@@ -26,7 +26,7 @@ main() {
     // Every 100 lines, clear the display and update the counter.
     lineCounter += 1;
     if ((lineCounter % 100) == 0) {
-      display.clear(Color.black);
+      display.clear();
       display.writeText(10, 10, 'Rendered $lineCounter lines');
     }
   }