usb: r8a66597-udc: Add processing when USB was removed.

When USB was removed, this patch prepares for the next insertion.

Signed-off-by: Yusuke Goda <yusuke.goda.sx@renesas.com>
Acked-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Cc: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>