vfb: use fb_sys_read() and fb_sys_write()

Since vfb's framebuffer is vmalloc'ed, use the fb_sys_read() and
fb_sys_write().

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/video/Kconfig b/drivers/video/Kconfig
index 5e3492c..75ec7d1 100644
--- a/drivers/video/Kconfig
+++ b/drivers/video/Kconfig
@@ -1743,6 +1743,7 @@
 	select FB_SYS_FILLRECT
 	select FB_SYS_COPYAREA
 	select FB_SYS_IMAGEBLIT
+	select FB_SYS_FOPS
 	---help---
 	  This is a `virtual' frame buffer device. It operates on a chunk of
 	  unswappable kernel memory instead of on the memory of a graphics