virgl: Fix VIRGL_OBJ_SAMPLE_STATE_S0_MAX_ANISOTROPY
requested to merge akihiko.odaki/virglrenderer:virgl-fix-virgl_obj_sample_state_s0_max_anisotropy into master
The new definition is copied from commit 2116a4f5cc3a570a30a1378d03dbe5bd9c1ae50c of Mesa.
Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>