bootloader: fix wrong return for versions endpoint

The endpoint provides firmware and signing pubkeys versions, but
the function was returning the lenght of three versions struct,
instead of two.

src/bootloader/bootloader.c

@@ -733,7 +733,7 @@ static size_t _api_set_show_firmware_hash(const uint8_t* input, uint8_t* output)
 }
 
 /*
- * output filled with bootloader version | firmware version | signing pubkeys version
+ * output filled with firmware version | signing pubkeys version
  */
 static size_t _api_versions(uint8_t* output)
 {
@@ -744,7 +744,7 @@ static size_t _api_versions(uint8_t* output)
         (const uint8_t*)&data->fields.signing_pubkeys_version,
         sizeof(version_t));
     _report_status(OP_STATUS_OK, output);
-    return BOOT_OP_LEN + sizeof(version_t) * 3;
+    return BOOT_OP_LEN + sizeof(version_t) * 2;
 }
 
 static void _api_reboot(void)