stub: fix typo in method name (#12356)

Author: benjaminp

stub/src/main/java/io/grpc/stub/ClientCalls.java

@@ -931,7 +931,7 @@ public <T> void waitAndDrainWithTimeout(boolean waitForever, long end,
         } while ((runnable = poll()) != null);
         // Wake everything up now that we've done something and they can check in their outer loop
         // if they can continue or need to wait again.
-        signallAll();
+        signalAll();
       }
     }
 
@@ -949,11 +949,11 @@ public void drain() throws InterruptedException {
       }
 
       if (didWork) {
-        signallAll();
+        signalAll();
       }
     }
 
-    private void signallAll() {
+    private void signalAll() {
       waiterLock.lock();
       try {
         waiterCondition.signalAll();