tree: always initialize ns variable

With some more aggressive CFLAGS/LDFLAGS optimized for size the compiler
gets confused and can't figure out if 'n' is initialized or not.

../libnvme/src/nvme/tree.c: In function ‘__nvme_scan_namespace’:
../libnvme/src/nvme/tree.c:2598:22: error: ‘n’ may be used uninitialized [-Werror=maybe-uninitialized]
 2598 |         n->sysfs_dir = path;
      |         ~~~~~~~~~~~~~^~~~~~
../libnvme/src/nvme/tree.c:2583:25: note: ‘n’ was declared here
 2583 |         struct nvme_ns *n;
      |                         ^

Signed-off-by: Daniel Wagner <[email protected]>

Author: igaw

libnvme/src/nvme/tree.c

@@ -2573,7 +2573,7 @@ static int __nvme_scan_namespace(struct nvme_global_ctx *ctx,
 {
 	_cleanup_free_ char *blkdev = NULL;
 	_cleanup_free_ char *path = NULL;
-	struct nvme_ns *n;
+	struct nvme_ns *n = NULL;
 	int ret;
 
 	blkdev = nvme_ns_generic_to_blkdev(name);