Missing parens in REQUEST_FIXED_SIZE macro [CVE-2014-8092 pt. 5]

The 'n' parameter must be surrounded by parens in both places to
prevent precedence from mis-computing things.
Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>

include/dix.h

@@ -80,7 +80,7 @@ SOFTWARE.
 
 #define REQUEST_FIXED_SIZE(req, n)\
     if (((sizeof(req) >> 2) > client->req_len) || \
-        ((n >> 2) >= client->req_len) || \
+        (((n) >> 2) >= client->req_len) ||                              \
         ((((uint64_t) sizeof(req) + (n) + 3) >> 2) != (uint64_t) client->req_len))  \
          return(BadLength)