cr50_utils: fix string formatting error

BUG=none
BRANCH=none
TEST=none

Change-Id: I521f212cae26f39d5c8e8acf5942262e0eba688b
Signed-off-by: Mary Ruthven <mruthven@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/540127
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>
diff --git a/client/common_lib/cros/cr50_utils.py b/client/common_lib/cros/cr50_utils.py
index b61e37e..6c40c94 100644
--- a/client/common_lib/cros/cr50_utils.py
+++ b/client/common_lib/cros/cr50_utils.py
@@ -172,7 +172,7 @@
     if result.exit_status and result.exit_status != UPDATE_OK:
         logging.debug(result)
         raise error.TestError("Unexpected usb_update exit code after %s %d" %
-                              ' '.join(args), result.exit_status)
+                              (' '.join(args), result.exit_status))
     return result