MIPS: Loongson3: Fix __node_distances undefined error

export the __node_distances symbol in the loongson3 numa code to fix the
build error:

  Building modules, stage 2.
  MODPOST 221 modules
ERROR: "__node_distances" [drivers/block/nvme.ko] undefined!
scripts/Makefile.modpost:90: recipe for target '__modpost' failed

when building the kernel with:
 CONFIG_CPU_LOONGSON3=y
 CONFIG_NUMA=y
 CONFIG_BLK_DEV_NVME=m
Signed-off-by: James Cowgill <James.Cowgill@imgtec.com>
Cc: <stable@vger.kernel.org> # v3.17+
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Huacai Chen <chenhc@lemote.com>
Cc: linux-mips@linux-mips.org
Cc: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Patchwork: https://patchwork.linux-mips.org/patch/8444/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/loongson/loongson-3/numa.c

@@ -33,6 +33,7 @@
 
 static struct node_data prealloc__node_data[MAX_NUMNODES];
 unsigned char __node_distances[MAX_NUMNODES][MAX_NUMNODES];
+EXPORT_SYMBOL(__node_distances);
 struct node_data *__node_data[MAX_NUMNODES];
 EXPORT_SYMBOL(__node_data);