Fix build: fprintf without modifier

Change-Id: I66ae21a25a25fa3c70837bc54a7d406182d4cf37
diff --git a/updater/install.c b/updater/install.c
index da6b577..4a0e064 100644
--- a/updater/install.c
+++ b/updater/install.c
@@ -65,8 +65,7 @@
     // The recovery will only print the contents to screen for pipe command
     // ui_print. We need to dump the contents to stderr (which has been
     // redirected to the log file) directly.
-    fprintf(stderr, buffer);
-    fprintf(stderr, "\n");
+    fprintf(stderr, "%s", buffer);
 }
 
 __attribute__((__format__(printf, 2, 3))) __nonnull((2))