Fix an uninitialized data access

zfs_acl_node_alloc allocates an uninitialized data buffer, but upstack
zfs_acl_chmod only partially initializes it.  KMSAN reported that this
memory remained uninitialized at the point when it was read by
lzjb_compress, which suggests a possible kernel memory disclosure bug.

The full KMSAN warning may be found in the PR.
openzfs#16511

Signed-off-by:	Alan Somers <asomers@gmail.com>
Sponsored by:	Axcient

module/os/freebsd/zfs/zfs_acl.c

@@ -473,7 +473,7 @@ zfs_acl_node_alloc(size_t bytes)
 
 	aclnode = kmem_zalloc(sizeof (zfs_acl_node_t), KM_SLEEP);
 	if (bytes) {
-		aclnode->z_acldata = kmem_alloc(bytes, KM_SLEEP);
+		aclnode->z_acldata = kmem_zalloc(bytes, KM_SLEEP);
 		aclnode->z_allocdata = aclnode->z_acldata;
 		aclnode->z_allocsize = bytes;
 		aclnode->z_size = bytes;

module/os/linux/zfs/zfs_acl.c

@@ -471,7 +471,7 @@ zfs_acl_node_alloc(size_t bytes)
 
 	aclnode = kmem_zalloc(sizeof (zfs_acl_node_t), KM_SLEEP);
 	if (bytes) {
-		aclnode->z_acldata = kmem_alloc(bytes, KM_SLEEP);
+		aclnode->z_acldata = kmem_zalloc(bytes, KM_SLEEP);
 		aclnode->z_allocdata = aclnode->z_acldata;
 		aclnode->z_allocsize = bytes;
 		aclnode->z_size = bytes;