wifi: iwlwifi: mei: fix potential NULL-ptr deref after clone

If cloning the SKB fails, don't try to use it, but rather return
as if we should pass it.

Coverity CID: 1503456

Fixes: 2da4366f ("iwlwifi: mei: add the driver to allow cooperation with CSME")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Gregory Greenman <gregory.greenman@intel.com>
Link: https://lore.kernel.org/r/20221030191011.0ce03ba99601.I87960b7cb0a3d16b9fd8d9144027e7e2587f5a58@changeid