mediafoundation: fix deadlock when user call shutdown and endGetEvent concurrently

The issue occurs when 'IMFShutdown::Shutdown' is called on MFT on one thread and IMFMediaEventGenerator::EndGetEvent' is called on another thread.
Shutdown is taking a lock (m_lockShutdown), changes m_bShutdown to true, then calls OnFlush which takes API lock (m_lock)
EndGetEvent and all other API's take an API lock (m_lock), then calls checkshutdownstatus() which takes the m_lockShutdown.
So if Shutdown acquires m_lockShutdown and prior to acquiring API lock, and EndGetEvent acquire m_lock, then we have deadlock on m_lockShutdown.  Since the CheckShutdownStatus is only checking the m_bShutdown variable, it really doesn't have to be protected by the shutdown  lock.

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Reviewed-by: Yubo Xie <yuboxie@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36507>

src/gallium/frontends/mediafoundation/mfshutdown.cpp

@@ -28,7 +28,6 @@
 HRESULT
 CDX12EncHMFT::CheckShutdown( void )
 {
-   std::lock_guard<std::mutex> lock( m_lockShutdown );
    if( m_bShutdown )
    {
       return MF_E_SHUTDOWN;