netlabel: fix an uninitialized warning in netlbl_unlabel_staticlist()

Static checking revealed that a previous fix to
netlbl_unlabel_staticlist() leaves a stack variable uninitialized,
this patches fixes that.

Fixes: 866358ec

 ("netlabel: fix our progress tracking in netlbl_unlabel_staticlist()")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Link: https://lore.kernel.org/r/160530304068.15651.18355773009751195447.stgit@sifl
Signed-off-by: Jakub Kicinski <kuba@kernel.org>