drm: Populate fb->dev from drm_helper_mode_fill_fb_struct()

Populating fb->dev before drm_framebuffer_init() allows us to use
fb->dev already while validating the framebuffer. Let's have
drm_helper_mode_fill_fb_struct() do that for us.

Also make drm_framebuffer_init() warn us if a different device
pointer is passed to it than was passed to
drm_helper_mode_fill_fb_struct().

v2: Reject fbs with invalid fb->dev (Laurent)

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com> (v1)
Link: http://patchwork.freedesktop.org/patch/msgid/1479498793-31021-19-git-send-email-ville.syrjala@linux.intel.com