efi_loader: Drop sandbox PXE architecture

Rather than returning 0, just return an error, since sandbox is not used
with PXE at present.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/efi_loader/efi_helper.c b/lib/efi_loader/efi_helper.c
index ab5678e..bf96f61 100644
--- a/lib/efi_loader/efi_helper.c
+++ b/lib/efi_loader/efi_helper.c
@@ -91,8 +91,6 @@
 		return 0x19;
 	else if (IS_ENABLED(CONFIG_ARCH_RV64I))
 		return 0x1b;
-	else if (IS_ENABLED(CONFIG_SANDBOX))
-		return 0;	/* not used */
 
 	return -EINVAL;
 }