localize input mfxFrameSurface1* for scale_qsv

[YaboWei]

If scale_qsv + enc and ONLY enc called by different thread, ONLY enc may got a Locked mfxFrameSurface1(

Intel_FFmpeg_plugins/libavcodec/qsvenc.c

Line 1120 in bd1a484

qf->surface = *(mfxFrameSurface1*)qf->frame->data[3];

) which is Locked by scale_qsv + enc's scale_qsv, and this surf would never be Unlocked, and this surf in qsv_pool(

Intel_FFmpeg_plugins/libavutil/hwcontext_qsv.c

Line 379 in bd1a484

static int qsv_init_pool(AVHWFramesContext *ctx, uint32_t fourcc)

) is "leak".

If scale_qsv also localize input surf like enc, ONLY enc would never got a Locked mfxFrameSurface1, it's OK.

[lizhong1008]

Patch looks good expect need a better commit message.