iris: Properly handle new unbind_num_trailing_slots parameters

iris: Properly handle new unbind_num_trailing_slots parameters

Commits 0278d1fa323cf1f289..b688ea31fcf7e20436 added a new parameter
to set_vertex_buffers(), set_shader_images(), and set_sampler_views()
which specifies a number of trailing slots to unbind.  They updated
the iris functions to do the unbinding, but didn't update the code
to mark which things are bound in the bitfields.  This meant that
later code would assume those unbound slots were bound, and crash
on a NULL dereference.  All that's needed is to add that slot count
when unbinding things in the bitfield.

Fixes: 0278d1fa323 ("gallium: add unbind_num_trailing_slots to set_vertex_buffers")
Fixes: 72ff66c3d73 ("gallium: add unbind_num_trailing_slots to set_shader_images")
Fixes: b688ea31fcf ("gallium: add unbind_num_trailing_slots to set_sampler_views")
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8758>