framebuffer: Fix locking

The gralloc locking did not lock
the framebuffer. Use genlock to
lock the framebuffers.

Change-Id: Ie8be6f7950f6df06a2293c3df863e19cd5386479
diff --git a/libgralloc/fb_priv.h b/libgralloc/fb_priv.h
index 628a961..83b941a 100644
--- a/libgralloc/fb_priv.h
+++ b/libgralloc/fb_priv.h
@@ -47,7 +47,7 @@
     uint32_t numBuffers;
     uint32_t bufferMask;
     pthread_mutex_t lock;
-    buffer_handle_t currentBuffer;
+    private_handle_t *currentBuffer;
     struct fb_var_screeninfo info;
     struct fb_fix_screeninfo finfo;
     float xdpi;