efi_loader: Update startimage_exit self-test to check error

Check for an error returned from the decompress() function, just in
case.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

lib/efi_selftest/efi_selftest_startimage_exit.c

@@ -84,13 +84,15 @@ static efi_status_t decompress(u8 **image)
 static int setup(const efi_handle_t handle,
 		 const struct efi_system_table *systable)
 {
+	efi_status_t ret;
+
 	image_handle = handle;
 	boottime = systable->boottime;
 
 	/* Load the application image into memory */
-	decompress(&image);
+	ret = decompress(&image);
 
-	return EFI_ST_SUCCESS;
+	return ret;
 }
 
 /*