Print error message if of_state_fixup() fails

If of_state_fixup() fails for some reason, boot/bootm will fail, too

However, it is completely unclear where the error has happened, and to
the user it rather seems like the kernel device tree loaded from some
file was broken/corrupt, not that in fact some fixup routine was
failing.

Adding a meaningful error message can help debugging significantly.

Signed-off-by: Harald Welte <laforge@gnumonks.org>

common/state.c

@@ -785,6 +785,7 @@ static int of_state_fixup(struct device_node *root, void *ctx)
 	return 0;
 
  out:
+	dev_err(&state->dev, "error fixing up device tree with boot state\n");
 	of_delete_node(new_node);
 	return ret;
 }