set ep to NULL to avoid double close

Per suggestion of @awlauria

Signed-off-by: Harumi Kuno <harumi.kuno@hpe.com>

opal/mca/btl/ofi/btl_ofi_component.c

@@ -584,6 +584,7 @@ fail:
     /* close basic ep before closing av */
     if (NULL != ep && !module->is_scalable_ep) {
         fi_close(&ep->fid);
+        ep = NULL;
     }
 
     /* if the contexts have not been initiated, num_contexts should