Fix negative wait for bootloader time.

Bug 3110915

Change-Id: I4b46a14ecfc02d8289465ff5ed12815915291d0e
diff --git a/src/com/android/tradefed/device/DeviceStateMonitor.java b/src/com/android/tradefed/device/DeviceStateMonitor.java
index e53b309..a05e1ea 100644
--- a/src/com/android/tradefed/device/DeviceStateMonitor.java
+++ b/src/com/android/tradefed/device/DeviceStateMonitor.java
@@ -286,7 +286,12 @@
         long elapsedTime = System.currentTimeMillis() - startTime;
         IFastbootListener listener = new StubFastbootListener();
         mMgr.addFastbootListener(listener);
-        boolean result =  waitForDeviceState(TestDeviceState.FASTBOOT, time - elapsedTime);
+        long waitTime = time - elapsedTime;
+        if (waitTime < 0) {
+            // wait at least 200ms
+            waitTime = 200;
+        }
+        boolean result =  waitForDeviceState(TestDeviceState.FASTBOOT, waitTime);
         mMgr.removeFastbootListener(listener);
         return result;
     }