Actually unresolve .plt slot when the post-update breakpoint hits

The clever optimization from two days ago actually broke things as my test
case was doing a lot of one-off calls and I never noticed that it breaks
the common case.
diff --git a/sysdeps/linux-gnu/ppc/plt.c b/sysdeps/linux-gnu/ppc/plt.c
index 4aea42d..7e19441 100644
--- a/sysdeps/linux-gnu/ppc/plt.c
+++ b/sysdeps/linux-gnu/ppc/plt.c
@@ -558,6 +558,9 @@
 	if (read_plt_slot_value(proc, libsym->arch.plt_slot_addr, &value) < 0)
 		return;
 
+	unresolve_plt_slot(proc, libsym->arch.plt_slot_addr,
+			   libsym->arch.resolved_value);
+
 	/* cb_on_all_stopped looks if HANDLER is set to NULL as a way
 	 * to check that this was run.  It's an error if it
 	 * wasn't.  */