i965: fix build warning on clang

fixes following warning:
   warning: format specifies type 'long' but the argument has type 'uint64_t' (aka 'unsigned long long')

cast is needed to avoid this change turning in to another warning:
   warning: format specifies type 'unsigned long long' but the argument has type 'uint64_t' (aka 'unsigned long')

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

src/mesa/drivers/dri/i965/brw_bufmgr.c

@@ -396,7 +396,8 @@ retry:
 
    pthread_mutex_unlock(&bufmgr->lock);
 
-   DBG("bo_create: buf %d (%s) %ldb\n", bo->gem_handle, bo->name, size);
+   DBG("bo_create: buf %d (%s) %llub\n", bo->gem_handle, bo->name,
+       (unsigned long long) size);
 
    return bo;