Change order of error message printed when gdbserver can't find CWD

I forgot to address Pedro's comment about my last patch and change the
order of the message printed when getcwd returns NULL on gdbserver.
This obvious commit does it.

gdb/gdbserver/ChangeLog:
2018-02-28  Sergio Durigan Junior  <sergiodj@redhat.com>

	* server.c (captured_main): Change order of error message printed
	when the current working directory cannot be found.

gdb/gdbserver/server.c

@@ -3573,7 +3573,7 @@ captured_main (int argc, char *argv[])
   current_directory = getcwd (NULL, 0);
   if (current_directory == NULL)
     {
-      error (_("%s: error finding working directory"),
+      error (_("Could not find current working directory: %s"),
 	     safe_strerror (errno));
     }