staging: fbtft: core: set smem_len before fb_deferred_io_init call

The fbtft_framebuffer_alloc() calls fb_deferred_io_init() before
initializing info->fix.smem_len. It is set to zero by the
framebuffer_alloc() function. It will trigger a WARN_ON() at the
start of fb_deferred_io_init() and the function will not do anything.

Fixes: 856082f021a2 ("fbdev: defio: fix the pagelist corruption")
Signed-off-by: Peter Suti <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/fbtft/fbtft-core.c

···
 	fbdefio->delay =            HZ / fps;
 	fbdefio->sort_pagereflist = true;
 	fbdefio->deferred_io =      fbtft_deferred_io;
-	fb_deferred_io_init(info);
 
 	snprintf(info->fix.id, sizeof(info->fix.id), "%s", dev->driver->name);
 	info->fix.type =           FB_TYPE_PACKED_PIXELS;
···
 	info->fix.line_length =    width * bpp / 8;
 	info->fix.accel =          FB_ACCEL_NONE;
 	info->fix.smem_len =       vmem_size;
+	fb_deferred_io_init(info);
 
 	info->var.rotate =         pdata->rotate;
 	info->var.xres =           width;