drm/nouveau: fix u32 overflow in pushbuf reloc bounds check

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

drm/nouveau: fix u32 overflow in pushbuf reloc bounds check

nouveau_gem_pushbuf_reloc_apply() validates each relocation with

if (r->reloc_bo_offset + 4 > nvbo->bo.base.size)

but reloc_bo_offset is __u32 (uapi/drm/nouveau_drm.h) and the integer

literal 4 promotes to unsigned int, so the addition is performed in 32

bits and wraps before the comparison against the size_t bo size.

Cast to u64 so the addition happens in 64-bit arithmetic.

[ Add Fixes: tag. - Danilo ]