wl1271: Fix ad-hoc SSID update

If re-configuring the SSID while ad-hoc was already enabled, the beacon
template would be properly updated, but the SSID passed in the CMD_JOIN would
not - hence filtering etc would not work properly.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>