v3d: Don't try to update the shadow texture for separate stencil.

v3d: Don't try to update the shadow texture for separate stencil.

There are two cases where v3d's sampler view's resource doesn't match the
base's: shadow textures for sampling from raster, and pointing at the
separate depth texture for z32f_s8x24.  We only want to update shadow for
the first case.

Fixes
dEQP-GLES31.functional.stencil_texturing.render.depth32f_stencil8_draw
when run after the previous testcase.