CVE-2026-74417: drm/radeon: fix integer overflow in radeon_align_pitch()

In the Linux kernel, the following vulnerability has been resolved:

drm/radeon: fix integer overflow in radeonalignpitch()

radeonalignpitch() has the same kind of overflow issue as the old amdgpu helper: both the alignment round-up add and the final 'aligned cpp' calculation can overflow signed int.

If that wraps, radeonmodedumbcreate() can end up returning an invalid pitch or creating a zero-sized dumb buffer.

Fix this by using checkaddoverflow() for the alignment round-up and checkmuloverflow() for the final pitch calculation, returning 0 on overflow. Also reject zero pitch and size in radeonmodedumbcreate().

Found via AST-based call-graph analysis using sqry.