fbdev/vfb: Use struct fb_info.screen_buffer

Use info->screen_buffer when reading and writing framebuffers in
system memory. It's the correct pointer for this address space.

The struct fb_info has a union to store the framebuffer memory. This can
either be info->screen_base if the framebuffer is stored in I/O memory,
or info->screen_buffer if the framebuffer is stored in system memory.

As the driver operates on the latter address space, it is wrong to use
.screen_base and .screen_buffer must be used instead. This also gets
rid of casting needed due to not using the correct data type.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230428122452.4856-13-tzimmermann@suse.de

drivers/video/fbdev/vfb.c

@@ -439,7 +439,7 @@ static int vfb_probe(struct platform_device *dev)
 	if (!info)
 		goto err;
 
-	info->screen_base = (char __iomem *)videomemory;
+	info->screen_buffer = videomemory;
 	info->fbops = &vfb_ops;
 
 	if (!fb_find_mode(&info->var, info, mode_option,