Use correct format specifier

Discovered by the upcoming compiler update.

Test: m checkbuild
Change-Id: I8dd4bb711bfa4f4b71a3345a2ee38f689cee5257
diff --git a/trusty/storage/proxy/storage.c b/trusty/storage/proxy/storage.c
index c61e89d..5b83e21 100644
--- a/trusty/storage/proxy/storage.c
+++ b/trusty/storage/proxy/storage.c
@@ -379,7 +379,7 @@
     }
 
     if (req->size > MAX_READ_SIZE) {
-        ALOGW("%s: request is too large (%zd > %zd) - refusing\n",
+        ALOGW("%s: request is too large (%u > %d) - refusing\n",
               __func__, req->size, MAX_READ_SIZE);
         msg->result = STORAGE_ERR_NOT_VALID;
         goto err_response;