dm ioctl: prevent potential spectre v1 gadget
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v4.14.276 by commit 58880025e3362024f6d8ea01cb0c7a5df6c84ba6. For more details please see the references link.