wlcore: set 5Ghz probe-req template for DFS channels

Even passive scans on DFS channels require us to send probe requests, so
configure the probe-req in this case.

Also use this opportunity to prevent the code from crashing in case no
SSIDs are sent from above. This will likely happen in the DFS case
introduced. Even a passive scan might need the probe request configured
because of DFS channels.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>