[FFmpeg-cvslog] lavu: add calling convention for OpenCL callback.

[Ruiling Song]

ffmpeg | branch: master | Ruiling Song <ruiling.song at intel.com> | Wed Jun  6 23:31:44 2018 +0800| [e4006a474f689ef9534448d3382d220c62b413b6] | committer: Mark Thompson

lavu: add calling convention for OpenCL callback.

This fix a build error on Windows:
C2440: connot convert from 'void (__cdecl *) (...)' to 'void (__stdcall *)(...)'.

Signed-off-by: Ruiling Song <ruiling.song at intel.com>

> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=e4006a474f689ef9534448d3382d220c62b413b6
---

 libavutil/hwcontext_opencl.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/libavutil/hwcontext_opencl.c b/libavutil/hwcontext_opencl.c
index 43b5c5ae0c..e08d7bcb9b 100644
--- a/libavutil/hwcontext_opencl.c
+++ b/libavutil/hwcontext_opencl.c
@@ -141,9 +141,10 @@ typedef struct OpenCLFramesContext {
 } OpenCLFramesContext;
 
 
-static void opencl_error_callback(const char *errinfo,
-                                  const void *private_info, size_t cb,
-                                  void *user_data)
+static void CL_CALLBACK opencl_error_callback(const char *errinfo,
+                                              const void *private_info,
+                                              size_t cb,
+                                              void *user_data)
 {
     AVHWDeviceContext *ctx = user_data;
     av_log(ctx, AV_LOG_ERROR, "OpenCL error: %s\n", errinfo);