Avoid uninitialized map, flags in ext.

This function returns a stack pointer to a struct scoutfs_extent, after
setting start, len to an extent found in the proper zone, but it leaves
map and flags members unset.

Initialize the struct to {0,} avoids passing uninitialized values up the
callstack.

Signed-off-by: Auke Kok <auke.kok@versity.com>

kmod/src/alloc.c

@@ -857,7 +857,7 @@ static int find_zone_extent(struct super_block *sb, struct scoutfs_alloc_root *r
 		.zone = SCOUTFS_FREE_EXTENT_ORDER_ZONE,
 	};
 	struct scoutfs_extent found;
-	struct scoutfs_extent ext;
+	struct scoutfs_extent ext = {0,};
 	u64 start;
 	u64 len;
 	int nr;