hwcontext: Perform usual initialisation on derived device contexts

The initialisation should be common.  For libmfx, it was previously
happening in the derivation function and this moves it out.

libavutil/hwcontext.c

@@ -645,6 +645,10 @@ int av_hwdevice_ctx_create_derived(AVBufferRef **dst_ref_ptr,
     goto fail;
 
 done:
+    ret = av_hwdevice_ctx_init(dst_ref);
+    if (ret < 0)
+        goto fail;
+
     *dst_ref_ptr = dst_ref;
     return 0;
 

libavutil/hwcontext_qsv.c

@@ -989,7 +989,6 @@ static int qsv_device_derive_from_child(AVHWDeviceContext *ctx,
                                         int flags)
 {
     AVQSVDeviceContext *hwctx = ctx->hwctx;
-    QSVDeviceContext       *s = ctx->internal->priv;
 
     mfxVersion    ver = { { 3, 1 } };
     mfxHDL        handle;
@@ -1058,16 +1057,6 @@ static int qsv_device_derive_from_child(AVHWDeviceContext *ctx,
         goto fail;
     }
 
-    ret = qsv_device_init(ctx);
-    if (ret < 0)
-        goto fail;
-    if (s->handle_type != handle_type) {
-        av_log(ctx, AV_LOG_ERROR, "Error in child device handle setup: "
-               "type mismatch (%d != %d).\n", s->handle_type, handle_type);
-        err = AVERROR_UNKNOWN;
-        goto fail;
-    }
-
     return 0;
 
 fail: