selftests/efivarfs: Add checking of the test return value

Add checking of the test return value, otherwise it will report success
forever for test_create_read().

Fixes: dff6d2ae56d0 ("selftests/efivarfs: clean up test files from test_create*()")
Signed-off-by: Zhao Gongyi <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/efivarfs/efivarfs.sh

···
 {
 	local file=$efivarfs_mount/$FUNCNAME-$test_guid
 	./create-read $file
+	if [ $? -ne 0 ]; then
+		echo "create and read $file failed"
+		file_cleanup $file
+		exit 1
+	fi
 	file_cleanup $file
 }