crosperf: fix --help

This is a format string; without this, --help raises
ValueError: unsupported format character ',' (0x2c) at index 311

BUG=None
TEST=crosperf --help

Change-Id: I5fbdb996888156f8a1531c2b140c3f734be7edff
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/toolchain-utils/+/2173547
Reviewed-by: Manoj Gupta <manojgupta@chromium.org>
Tested-by: George Burgess <gbiv@chromium.org>
diff --git a/crosperf/settings_factory.py b/crosperf/settings_factory.py
index 20ab2ad..cfc4013 100644
--- a/crosperf/settings_factory.py
+++ b/crosperf/settings_factory.py
@@ -365,8 +365,8 @@
             ' data.\n'
             'With 0 - do not run top.\n'
             'NOTE: Running top with interval 1-5 sec has insignificant'
-            ' performance impact (performance degradation does not exceed 0.3%,'
-            ' measured on x86_64, ARM32, and ARM64).',
+            ' performance impact (performance degradation does not exceed'
+            ' 0.3%%, measured on x86_64, ARM32, and ARM64).',
             required=False,
             default=0))
     self.AddField(