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: f178e96d ("arch: Remove struct fb_info from video helpers")
Reported-by: Arthur Borsboom <arthurborsboom@gmail.com>
Closes: https://lore.kernel.org/xen-devel/CALUcmUncX=LkXWeiSiTKsDY-cOe8QksWhFvcCneOKfrKd0ZajA@mail.gmail.com/


Tested-by: Arthur Borsboom <arthurborsboom@gmail.com>
CC: stable@vger.kernel.org
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Helge Deller <deller@gmx.de>