efi_selftest: add missing line feed in efi_selftest_miniapp_exit

If an error occurs we may see an output like:

    EFI application calling Exit

    Could not open loaded image protocolLoaded image protocol missing

Add the missing line feed.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/lib/efi_selftest/efi_selftest_miniapp_exit.c b/lib/efi_selftest/efi_selftest_miniapp_exit.c
index 8b2e60c..0909a5c 100644
--- a/lib/efi_selftest/efi_selftest_miniapp_exit.c
+++ b/lib/efi_selftest/efi_selftest_miniapp_exit.c
@@ -39,7 +39,7 @@
 				  NULL, EFI_OPEN_PROTOCOL_GET_PROTOCOL);
 	if (ret != EFI_SUCCESS) {
 		cout->output_string(cout,
-				    u"Could not open loaded image protocol");
+				    u"Could not open loaded image protocol\n");
 		return ret;
 	}
 	if ((void *)check_loaded_image_protocol <