iwlwifi: mvm: squash a spurious warning on chnctx change

If the channel min-width changes, we can update the PHY ctx, even if
it has multiple references.

Signed-off-by: Arik Nemtsov <arik@wizery.com>
Reviewed-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>