qcacld-3.0: Remove calls to qdf_exit_thread()

Since Linux Kernel commit 63706172f332 ("kthreads: rework
kthread_stop()"), made in 2009 in Linux Kernel v2.6.31-rc1, it has not
been necessary for kernel threads to call do_exit(). Since we do not
support kernels earlier than that, remove the calls to
qdf_exit_thread(), the abstraction function for do_exit().

See Change-Id I22f27692fa8766df080630b9b0640c259285557c for more
information on why this call is being removed.

Change-Id: I5fa0e404e782edc04034bef8412acd0ca2f83097
CRs-Fixed: 3300457

core/dp/txrx3.0/dp_rx_thread.c

@@ -675,7 +675,6 @@ static int dp_rx_thread_loop(void *arg)
 	dp_info("exiting (%s) id %d pid %d", qdf_get_current_comm(),
 		rx_thread->id, qdf_get_current_pid());
 	qdf_event_set(&rx_thread->shutdown_event);
-	qdf_exit_thread(QDF_STATUS_SUCCESS);
 
 	return 0;
 }
@@ -753,7 +752,6 @@ static int dp_rx_refill_thread_loop(void *arg)
 	dp_info("exiting (%s) pid %d", qdf_get_current_comm(),
 		qdf_get_current_pid());
 	qdf_event_set(&rx_thread->shutdown_event);
-	qdf_exit_thread(QDF_STATUS_SUCCESS);
 
 	return 0;
 }