iwlwifi: mvm: be more forgiving if num of channels is too big

If number of channels in the driver is greater than
number of scan channels given by firmware TLV, do not
fail scan config, but adjust to firmware's number of channels.
This is helpful for supporting in driver new channels before
it being supported by firmware scan.

Signed-off-by: Shaul Triebitz <shaul.triebitz@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>