efi: Fix missing EFIAPI specifiers

These are missing in some functions. Add them to keep things consistent.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/include/efi_loader.h b/include/efi_loader.h
index 1bc3b33..871499f 100644
--- a/include/efi_loader.h
+++ b/include/efi_loader.h
@@ -95,7 +95,7 @@
  * Stub implementation for a protocol opener that just returns the handle as
  * interface
  */
-efi_status_t efi_return_handle(void *handle,
+efi_status_t EFIAPI efi_return_handle(void *handle,
 		efi_guid_t *protocol, void **protocol_interface,
 		void *agent_handle, void *controller_handle,
 		uint32_t attributes);