[mpp_list]: release the blocked thread at reset

The applcatiion thread is still blocking on the output port.

Change-Id: I4693125362a250e5d2f28af8226d608b3040f138
Signed-off-by: Randy Li <randy.li@rock-chips.com>

osal/mpp_list.cpp

@@ -241,6 +241,7 @@ RK_S32 mpp_list::flush()
             count--;
         }
     }
+    mCondition.signal();
     return 0;
 }