jfs: Fix array index bounds check in dbAdjTree

Bounds checking tools can flag a bug in dbAdjTree() for an array index
out of bounds in dmt_stree. Since dmt_stree can refer to the stree in
both structures dmaptree and dmapctl, use the larger array to eliminate
the false positive.

Signed-off-by: Dave Kleikamp <dave.kleikamp@oracle.com>
Reported-by: butt3rflyh4ck <butterflyhuangxx@gmail.com>
(cherry picked from commit c61b3e4)
CVE-2020-27815
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Timo Aaltonen <timo.aaltonen@canonical.com>

fs/jfs/jfs_dmap.h

@@ -183,7 +183,7 @@ typedef union dmtree {
 #define	dmt_leafidx	t1.leafidx
 #define	dmt_height	t1.height
 #define	dmt_budmin	t1.budmin
-#define	dmt_stree	t1.stree
+#define	dmt_stree	t2.stree
 
 /*
  *	on-disk aggregate disk allocation map descriptor.