dm ioctl: have constant on the right side of the test

[ Upstream commit 5cae0aa7 ]

Signed-off-by: Heinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@kernel.org>
Stable-dep-of: 249bed82 ("dm ioctl: Avoid double-fetch of version")
Signed-off-by: Sasha Levin <sashal@kernel.org>