r600g: fix bank swizzle calcs for scalar only operations.

r600g: fix bank swizzle calcs for scalar only operations.

In the initial code if we had nothing in the vector slots r would
never get reset to 0, so we'd fail to compile shaders, after the previous
commit this would happen for the LIT tests. When I fixed that we did a lot
of unnecessary loops through all the vector states when we had no vector
slots filled. So this patch optimises thing for the scalar only state.

This fixes the 3 LIT piglit tests on r600g.

Signed-off-by: Dave Airlie <airlied@redhat.com>