MIPS: Octeon: remove unnecessary null test before debugfs_remove_recursive

Fix checkpatch warning:
WARNING: debugfs_remove_recursive(NULL) is safe this check is probably not required

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Acked-by: David Daney <david.daney@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7224/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>