vrend: fix ubo id in vrend_draw_bind_ubo_shader

Chia-I Wu requested to merge olv/virglrenderer:virgl-bind-ubo into master

When there is no change to UBOs of a shader stage, we still need to increment ubo_id to match bind_ubo_locs. This was regressed by commit 2192c92f (renderer: only update dirty constbufs).

I noticed the issue when testing mesa/mesa!908 (merged).

CC @kusma @afrantzis @gurchetansingh

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