efi_loader: error code in UninstallProtocolInterface()

According to the UEFI specification UninstallProtocolInteface() has to
return EFI_NOT_FOUND if the interface is not found.

Correct the return value.

Cf. UEFI SCT II spec (2017), 3.3.2 UninstallProtocolInterface(), 5.1.3.2.4

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
diff --git a/lib/efi_loader/efi_boottime.c b/lib/efi_loader/efi_boottime.c
index b8589b9..b583ac6 100644
--- a/lib/efi_loader/efi_boottime.c
+++ b/lib/efi_loader/efi_boottime.c
@@ -514,7 +514,7 @@
 	if (ret != EFI_SUCCESS)
 		return ret;
 	if (handler->protocol_interface != protocol_interface)
-		return EFI_INVALID_PARAMETER;
+		return EFI_NOT_FOUND;
 	list_del(&handler->link);
 	free(handler);
 	return EFI_SUCCESS;