staging: r8712u: Fix problem when CONFIG_R8712_AP is set

When this driver was upgraded to the vendor 20100831 version in
commit 93c55dda et al,, one listhead initialization was missed.
This broke complete operation of the driver whenever AP mode was
enabled.

This patch fixes https://bugs.archlinux.org/task/27996

.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Cc: Stable <stable@vger.stable.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>