After refactoring of iris_bo_map_cpu and iris_bo_map_wc - immediate
return of NULL on failure to mmap a buffer was lost.
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/2855
Fixes: 5bc3f52dd8c2b5acaae959ccae2e1fb7c769bb22
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4786>