USB: r8a66597: clean up. remove unneeded null checks

td and dev can not be null.

Also they are dereferenced in list_for_each_entry_safe and list_for_each
before the check happens so we would have an oops if it were possible
for them to be null.

Found using the smatch static checker.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Yoshihiro Shimoda <shimoda.yoshihiro@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>