fbdev: xen-fbfront: Assign fb_info->device

Probing xen-fbfront faults in video_is_primary_device(). The passed-in
struct device is NULL since xen-fbfront doesn't assign it and the
memory is kzalloc()-ed. Assign fb_info->device to avoid this.

This was exposed by the conversion of fb_is_primary_device() to
video_is_primary_device() which dropped a NULL check for struct device.

Fixes: f178e96de7f0 ("arch: Remove struct fb_info from video helpers")
Reported-by: Arthur Borsboom <[e-mail]>
Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=[e-mail]/
Tested-by: Arthur Borsboom <[e-mail]>
CC: [e-mail]
Signed-off-by: Jason Andryuk <[e-mail]>
Reviewed-by: Roger Pau Monné <[e-mail]>
Reviewed-by: Thomas Zimmermann <[e-mail]>
Signed-off-by: Helge Deller <[e-mail]>

drivers/video/fbdev/xen-fbfront.c

···
 	/* complete the abuse: */
 	fb_info->pseudo_palette = fb_info->par;
 	fb_info->par = info;
+	fb_info->device = &dev->dev;
 
 	fb_info->screen_buffer = info->fb;