bio/bss_log.c: harmonize format string to silence -Wformat.

Reviewed-by: Richard Levitte <levitte@openssl.org>

crypto/bio/bss_log.c

@@ -322,7 +322,7 @@ static void xsyslog(BIO *bp, int priority, const char *string)
         break;
     }
 
-    sprintf(pidbuf, "[%u] ", GetCurrentProcessId());
+    sprintf(pidbuf, "[%lu] ", GetCurrentProcessId());
     lpszStrings[0] = pidbuf;
     lpszStrings[1] = string;