wl12xx: don't use WL1271_SCAN_OPT_PRIORITY_HIGH flag

When setting the WL1271_SCAN_OPT_PRIORITY_HIGH flag, the
driver requests a scan *now*, and the fw doesn't enter psm
before scanning, which in turn might cause packets loss.

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