ftp: fix incorrect out-of-memory code in Curl_pretransfer

- Return value type must match function type.

s/CURLM_OUT_OF_MEMORY/CURLE_OUT_OF_MEMORY/

Caught by Travis CI

lib/transfer.c

@@ -1391,7 +1391,7 @@ CURLcode Curl_pretransfer(struct SessionHandle *data)
       if(!wc->filelist) {
         result = Curl_wildcard_init(wc); /* init wildcard structures */
         if(result)
-          return CURLM_OUT_OF_MEMORY;
+          return CURLE_OUT_OF_MEMORY;
       }
     }