wl12xx: use dev_role_id for scans

Use device role for scans when the sta is not
associated.

sched_scan is used only when the sta is
not associated, and thus should use
the dev role (instead of sta role).

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