wl12xx: set scan probe requests rate according to the no_cck flag

Set the TX rate of probe requests during scanning according to the
no_cck flag in the scan request struct.

Signed-off-by: Guy Eilam <guy@wizery.com>
Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>