avfilter/vf_avgblur_opencl: fix error when clSetKernelArg fails

Fixes Coverity CID 1430382.

libavfilter/vf_avgblur_opencl.c

@@ -155,18 +155,21 @@ static int avgblur_opencl_filter_frame(AVFilterLink *inlink, AVFrame *input)
         if (cle != CL_SUCCESS) {
             av_log(avctx, AV_LOG_ERROR, "Failed to set kernel "
                    "destination image argument: %d.\n", cle);
+            err = AVERROR_UNKNOWN;
             goto fail;
         }
         cle = clSetKernelArg(ctx->kernel_horiz, 1, sizeof(cl_mem), &src);
         if (cle != CL_SUCCESS) {
             av_log(avctx, AV_LOG_ERROR, "Failed to set kernel "
                    "source image argument: %d.\n", cle);
+            err = AVERROR_UNKNOWN;
             goto fail;
         }
         cle = clSetKernelArg(ctx->kernel_horiz, 2, sizeof(cl_int), &radius_x);
         if (cle != CL_SUCCESS) {
             av_log(avctx, AV_LOG_ERROR, "Failed to set kernel "
                    "sizeX argument: %d.\n", cle);
+            err = AVERROR_UNKNOWN;
             goto fail;
         }
 
@@ -193,18 +196,21 @@ static int avgblur_opencl_filter_frame(AVFilterLink *inlink, AVFrame *input)
         if (cle != CL_SUCCESS) {
             av_log(avctx, AV_LOG_ERROR, "Failed to set kernel "
                    "destination image argument: %d.\n", cle);
+            err = AVERROR_UNKNOWN;
             goto fail;
         }
         cle = clSetKernelArg(ctx->kernel_vert, 1, sizeof(cl_mem), &inter);
         if (cle != CL_SUCCESS) {
             av_log(avctx, AV_LOG_ERROR, "Failed to set kernel "
                    "source image argument: %d.\n", cle);
+            err = AVERROR_UNKNOWN;
             goto fail;
         }
         cle = clSetKernelArg(ctx->kernel_vert, 2, sizeof(cl_int), &radius_y);
         if (cle != CL_SUCCESS) {
             av_log(avctx, AV_LOG_ERROR, "Failed to set kernel "
                    "sizeY argument: %d.\n", cle);
+            err = AVERROR_UNKNOWN;
             goto fail;
         }