correct vram dma timing in double speed

lib/src/processor/memory.rs

@@ -522,7 +522,7 @@ where
     C: PocketCamera + Send + 'static,
 {
     pub fn increment_timers(&mut self, machine_cycles: usize) {
-        let steps = (machine_cycles as usize) * 4;
+        let steps = machine_cycles * 4;
         self.cycle_count += steps;
 
         self.memory.oam_dma_tick(steps);

lib/src/processor/memory/mmio/cgb/vram_dma.rs

@@ -121,6 +121,10 @@ where
                 self.set(dest + i, self.get(source + i));
             }
         }
-        returning
+        if self.is_double_speed() {
+            returning * 2
+        } else {
+            returning
+        }
     }
 }