auxdisplay/cfag12864bfb: 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 <[e-mail]>
Reviewed-by: Javier Martinez Canillas <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/auxdisplay/cfag12864bfb.c

···
 	if (!info)
 		goto none;
 
-	info->screen_base = (char __iomem *) cfag12864b_buffer;
+	info->screen_buffer = cfag12864b_buffer;
 	info->screen_size = CFAG12864B_SIZE;
 	info->fbops = &cfag12864bfb_ops;
 	info->fix = cfag12864bfb_fix;