[SYCL] Fix memory leak (intel#1592)

The missing free calls caused memory leaks.

Signed-off-by: Byoungro So <[email protected]>

Author: bso-intel

SYCL/GroupAlgorithm/SYCL2020/reduce_over_group_size.cpp

@@ -109,4 +109,6 @@ int main() {
     printf("test failed!\n");
   }
   assert(fails == 0);
-}
+  free(x, ctx);
+  free(r, ctx);
+}