drm/i915/selftests: fix subtraction overflow bug
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 v5.18.13 by commit e8997d2d6b8d764e12489f1af2a1ce1d7384ca2a, it was introduced in version v4.12 by commit e1c5f754067b594de58d387aa5873dec83b6c9fd. For more details please see the references link.