Fix warnings.

Signed-off-by: Pol Henarejos <pol.henarejos@cttc.es>

src/fido/cmd_version.c

@@ -20,6 +20,6 @@
 
 int cmd_version() {
     memcpy(res_APDU, "U2F_V2", strlen("U2F_V2"));
-    res_APDU_size = strlen("U2F_V2");
+    res_APDU_size = (uint16_t)strlen("U2F_V2");
     return SW_OK();
 }