btl/openib: fix comment syntax, no code change

and silence gcc warning about nested comments

opal/mca/btl/openib/btl_openib_mca.c

@@ -790,7 +790,7 @@ int btl_openib_verify_mca_params (void)
     } else {
         mca_btl_openib_module.super.btl_flags &= ~MCA_BTL_FLAGS_CUDA_COPY_ASYNC_RECV;
     }
-#if 0 /* Disable this check for now while fork support code is worked out.
+#if 0 /* Disable this check for now while fork support code is worked out. */
     /* Cannot have fork support and GDR on at the same time.  If the user asks for both,
      * then print a message and return error.  If the user does not explicitly ask for
      * fork support, then turn it off in the presence of GDR.  */