radv/winsys: Fix offset in range merging.

If we change the virtual address we also have to change the offset in the buffer
to be mapped.

Fixes: 715df30a4e2 "radv/amdgpu: Add winsys implementation of virtual buffers."
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7953>
(cherry picked from commit d3286bdd764741b2cb6d30b59450ce9473884430)
2 files changed