[data-poll-sender] change StopFastPolls() to return void (#4941)

src/core/mac/data_poll_sender.cpp

@@ -378,10 +378,8 @@ void DataPollSender::SendFastPolls(uint8_t aNumFastPolls)
     }
 }
 
-otError DataPollSender::StopFastPolls(void)
+void DataPollSender::StopFastPolls(void)
 {
-    otError error = OT_ERROR_NONE;
-
     VerifyOrExit(mFastPollsUsers != 0, OT_NOOP);
 
     // If `mFastPollsUsers` hits the max, let it be cleared
@@ -390,13 +388,13 @@ otError DataPollSender::StopFastPolls(void)
 
     mFastPollsUsers--;
 
-    VerifyOrExit(mFastPollsUsers == 0, error = OT_ERROR_BUSY);
+    VerifyOrExit(mFastPollsUsers == 0, OT_NOOP);
 
     mRemainingFastPolls = 0;
     ScheduleNextPoll(kRecalculatePollPeriod);
 
 exit:
-    return error;
+    return;
 }
 
 void DataPollSender::ResetKeepAliveTimer(void)

src/core/mac/data_poll_sender.hpp

@@ -215,11 +215,8 @@ public:
     /**
      * This method asks data poll sender to stop fast polls when the expecting response is received.
      *
-     * @retval OT_ERROR_NONE            Successfully stopped fast polls when no other responses are expected.
-     * @retval OT_ERROR_BUSY            There are other callers who are waiting for responses.
-     *
      */
-    otError StopFastPolls(void);
+    void StopFastPolls(void);
 
     /**
      * This method gets the maximum data polling period in use.

src/core/thread/mle.cpp

@@ -2955,7 +2955,7 @@ void Mle::HandleDataResponse(const Message &aMessage, const Ip6::MessageInfo &aM
         // running out the specified number. E.g. other component also trigger fast poll, and
         // is waiting for response; or the corner case where multiple Mle Data Request attempts
         // happened due to the retransmission mechanism.
-        IgnoreError(Get<DataPollSender>().StopFastPolls());
+        Get<DataPollSender>().StopFastPolls();
     }
 
 exit: