USB: r8a66597-udc: Initialize uninitialized variable, fix compile warning

In today linux-next I got a compile warning due a possible uninitialized variable

This patch solves the issue initializing the variable


Signed-off-by: Javier Martinez Canillas <martinez.javier@gmail.com>
Cc: David Brownell <dbrownell@users.sourceforge.net>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Magnus Damm <damm@opensource.se>
Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>