ostree-prepare-root: Fix /etc bind mount

We were bind-mounting the initramfs' `/etc` (to itself) instead of the
target deployment `/etc` (to itself). Since we're already `chdir`'ed
into it, we can just drop the leading slash.

src/switchroot/ostree-prepare-root.c

@@ -251,7 +251,7 @@ main(int argc, char *argv[])
        * sysroot, we still need a writable /etc.  And to avoid race conditions
        * we ensure it's writable in the initramfs, before we switchroot at all.
        */
-      if (mount ("/etc", "/etc", NULL, MS_BIND, NULL) < 0)
+      if (mount ("etc", "etc", NULL, MS_BIND, NULL) < 0)
         err (EXIT_FAILURE, "failed to make /etc a bind mount");
       /* Pass on the fact that we discovered a readonly sysroot to ostree-remount.service */
       int fd = open (_OSTREE_SYSROOT_READONLY_STAMP, O_WRONLY | O_CREAT | O_CLOEXEC, 0644);