lavu/qsv: fix a random hwupload failure regression

Variable 'ret' hasn't been initialized，thus introducing a random
hwupload failure regression due to qsv session uninitialized.
Signed-off-by: Zhong Li <zhong.li@intel.com>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavutil/hwcontext_qsv.c

@@ -833,7 +833,7 @@ static int qsv_transfer_data_to(AVHWFramesContext *ctx, AVFrame *dst,
 
     mfxSyncPoint sync = NULL;
     mfxStatus err;
-    int ret;
+    int ret = 0;
 
     while (!s->session_upload_init && !s->session_upload && !ret) {
 #if HAVE_PTHREADS