avcodec/videotoolbox: set kCVPixelBufferIOSurfaceOpenGLTextureCompatibilityKey

Makes sure the output can be mapped as OpenGL texture.
This is what at least video players normally want.

libavcodec/videotoolbox.c

@@ -477,6 +477,7 @@ static CFDictionaryRef videotoolbox_buffer_attributes_create(int width,
     CFDictionarySetValue(buffer_attributes, kCVPixelBufferIOSurfacePropertiesKey, io_surface_properties);
     CFDictionarySetValue(buffer_attributes, kCVPixelBufferWidthKey, w);
     CFDictionarySetValue(buffer_attributes, kCVPixelBufferHeightKey, h);
+    CFDictionarySetValue(buffer_attributes, kCVPixelBufferIOSurfaceOpenGLTextureCompatibilityKey, kCFBooleanTrue);
 
     CFRelease(io_surface_properties);
     CFRelease(cv_pix_fmt);