iwlwifi: mvm: don't send GEO_TX_POWER_LIMIT on version < 41

Firmware versions before 41 don't support the GEO_TX_POWER_LIMIT
command, and sending it to the firmware will cause a firmware crash.
We allow this via debugfs, so we need to return an error value in case
it's not supported.

This had already been fixed during init, when we send the command if
the ACPI WGDS table is present.  Fix it also for the other,
userspace-triggered case.

Cc: stable@vger.kernel.org
Fixes: 7fe90e0e ("iwlwifi: mvm: refactor geo init")
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>