freedreno/ir3: fix neverball assert in case of unused VS inputs

freedreno/ir3: fix neverball assert in case of unused VS inputs

The logic to ensure VS and BS inputs are aligned wasn't accounting for
unused inputs in VS.  This *usually* doesn't happen, but it seems it
can in the case of ARB programs?

Fixes assert:
```
fd6_program_create: Assertion `bs->inputs[i].regid == vs->inputs[i].regid' failed.
```

Fixes: 882d53d8e36 ("freedreno/ir3+a6xx: same VBO state for draw/binning")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>