Run kernel_usb suites on ToT only.

BUG=None
TEST=None

Change-Id: I15f2f4b5c913b610a0accff5473f97e47df3f3ad
Reviewed-on: https://chromium-review.googlesource.com/294094
Reviewed-by: Sridhar Sonti <sontis@google.com>
Commit-Queue: Kalin Stoyanov <kalin@chromium.org>
Tested-by: Kalin Stoyanov <kalin@chromium.org>
diff --git a/suite_scheduler.ini b/suite_scheduler.ini
index 5de112b..f231234 100644
--- a/suite_scheduler.ini
+++ b/suite_scheduler.ini
@@ -413,14 +413,14 @@
 [NightlyKernelUsb]
 run_on: nightly
 suite: kernel_usb
-branch_specs: >=tot-2
+branch_specs: ==tot
 pool: kernel_usb
 file_bugs: True
 
 [NightlyKernelUsbSet1]
 run_on: nightly
 suite: kernel_usb_set1
-branch_specs: >=tot-2
+branch_specs: ==tot
 pool: kernel_usb_set1
 file_bugs: True