iwlwifi: don't send GEO_TX_POWER_LIMIT if no wgds table

The GEO_TX_POWER_LIMIT command was sent although
there is no wgds table, so the fw got wrong SAR values
from the driver.

Fix this by avoiding sending the command if no wgds
tables are available.

Signed-off-by: Golan Ben Ami <golan.ben.ami@intel.com>
Fixes: 39c1a972 ("iwlwifi: refactor the SAR tables from mvm to acpi")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Tested-By: Jonathan McDowell <noodles@earth.li>
Tested-by: Len Brown <len.brown@intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/iwlwifi.20200318081237.46db40617cc6.Id5cf852ec8c5dbf20ba86bad7b165a0c828f8b2e@changeid