nvc0/ir: output base for reading is based on laneid

nvc0/ir: output base for reading is based on laneid

PFETCH retrieves the address for incoming vertices, not output vertices
in TCS. For output vertices, we must use the laneid as a base.

Fixes barrier piglit test, which was failing for entirely non-barrier
reasons, but rather that it was (a) trying to draw multiple patches and
(b) the incoming patch size was not the same as the outgoing patch size.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>