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

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

crypto/bio/bss_log.c

diff --git a/crypto/bio/bss_log.c b/crypto/bio/bss_log.c
index f59ec7c..a86ea29 100644
--- a/crypto/bio/bss_log.c
+++ b/crypto/bio/bss_log.c
@@ -322,7 +322,7 @@
         break;
     }
 
-    sprintf(pidbuf, "[%u] ", GetCurrentProcessId());
+    sprintf(pidbuf, "[%lu] ", GetCurrentProcessId());
     lpszStrings[0] = pidbuf;
     lpszStrings[1] = string;