Fix two bugs related to opencl context.

1. As getDevice will implicitly call setDevice, in getContext we should not need to call it again.
2. Fix an incorrect type casting.

modules/ocl/src/initialization.cpp

@@ -930,8 +930,6 @@ namespace cv
                         clCxt.reset(new Context);
                     std::vector<Info> oclinfo;
                     CV_Assert(getDevice(oclinfo, CVCL_DEVICE_TYPE_ALL) > 0);
-                    oclinfo[0].impl->setDevice(0, 0, 0);
-                    clCxt.get()->impl = oclinfo[0].impl->copy();
 
                     *((volatile int*)&val) = 1;
                 }
@@ -1056,7 +1054,7 @@ BOOL WINAPI DllMain( HINSTANCE, DWORD  fdwReason, LPVOID )
         Context* cv_ctx = Context::getContext();
         if(cv_ctx)
         {
-            cl_context ctx = (cl_context)&(cv_ctx->impl->oclcontext);
+            cl_context ctx = cv_ctx->impl->oclcontext;
             if(ctx)
                 openCLSafeCall(clReleaseContext(ctx));
         }