carl9170: fix init-self regression

The commit: "carl9170: tx path review" introduced a regression.

gcc (with -Winit-self):
tx.c:1264: warning: ‘super’ is used uninitialized in this function

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>