fbdev: kyro: Validate overlay viewport coordinates

In the Linux kernel, the following vulnerability has been resolved: fbdev: kyro: Validate overlay viewport coordinates The overlay viewport end coordinates are computed from the viewport origin and dimensions using 32-bit unsigned arithmetic. Large input values can cause these calculations to wrap around before the resulting coordinates are passed to SetOverlayViewPort(). SetOverlayViewPort() packs the viewport coordinates into 16-bit register fields. The X coordinates are additionally adjusted by +2 and +1 before being written. Validate the coordinate calculations for 32-bit wraparound and ensure that the adjusted coordinates fit within their 16-bit register fields before calling SetOverlayViewPort(). Found by Linux Verification Center (linuxtesting.org) with SVACE.