fbdev: kill sparse warning in deferred IO

Kill the following in fb_defio.c:

drivers/video/fb_defio.c:40:43: warning: incorrect type in argument 1 (different address spaces)
drivers/video/fb_defio.c:40:43:    expected void *addr
drivers/video/fb_defio.c:40:43:    got char [noderef] *screen_base<asn:2>

The framebuffer memory of these types of devices are allocated from system
RAM.
Signed-off-by: NAntonino Daplas <adaplas@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/video/fb_defio.c

@@ -32,12 +32,14 @@ static struct page* fb_deferred_io_nopage(struct vm_area_struct *vma,
 	unsigned long offset;
 	struct page *page;
 	struct fb_info *info = vma->vm_private_data;
+	/* info->screen_base is in System RAM */
+	void *screen_base = (void __force *) info->screen_base;
 
 	offset = (vaddr - vma->vm_start) + (vma->vm_pgoff << PAGE_SHIFT);
 	if (offset >= info->fix.smem_len)
 		return NOPAGE_SIGBUS;
 
-	page = vmalloc_to_page(info->screen_base + offset);
+	page = vmalloc_to_page(screen_base + offset);
 	if (!page)
 		return NOPAGE_OOM;