libbb: make xchroot do a chdir("/") after chroot

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/runit/chpst.c b/runit/chpst.c
index 9b8c99b..ac296ba 100644
--- a/runit/chpst.c
+++ b/runit/chpst.c
@@ -417,8 +417,7 @@
 	}
 
 	if (opt & OPT_root) {
-		xchdir(root);
-		xchroot(".");
+		xchroot(root);
 	}
 
 	if (opt & OPT_u) {