net/caif/caif_socket.c: remove unnecessary null test before debugfs_remove_recursive

based on checkpatch:
"debugfs_remove_recursive(NULL) is safe this check is probably not required"

Cc: Dmitry Tarnyagin <dmitry.tarnyagin@lockless.no>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: netdev@vger.kernel.org
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: David S. Miller <davem@davemloft.net>