iwlwifi: don't use stack memory for kmem cache name

Since the kmem cache API doesn't internally allocate
the name but just points to the name that was passed
in we can't use stack memory for it. Move the name
into the transport struct.

Reported-by: Stanislaw Gruszka <sgruszka@redhat.com>
Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>