hwcontext: Do not call device_init again when deriving an existing device

The change in 309d6607 to call device_init
when doing derivation missed this case - we should only call it if we
actually made a new device.

libavutil/hwcontext.c

@@ -646,6 +646,9 @@ int av_hwdevice_ctx_create_derived(AVBufferRef **dst_ref_ptr,
                     ret = AVERROR(ENOMEM);
                     goto fail;
                 }
+                ret = av_hwdevice_ctx_init(dst_ref);
+                if (ret < 0)
+                    goto fail;
                 goto done;
             }
             if (ret != AVERROR(ENOSYS))
@@ -658,10 +661,6 @@ 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;