iwlwifi: bail out in case of bad trans state

In case of bad trans state (i.e. fw is not loaded) bail
out immediately instead of calling the trans, which might
not be fully initialized yet.

Also add WARN_ON_ONCE to help debugging where the errorneous
call is coming from.

Signed-off-by: Eliad Peller <eliadx.peller@intel.com>
Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>