selftests/efivarfs: create-read: fix a resource leak

[ Upstream commit 3f6f8a8c ]

The opened file should be closed in main(), otherwise resource
leak will occur that this problem was discovered by code reading

Signed-off-by: zhujun2 <zhujun2@cmss.chinamobile.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>