gk104/ir: sampler doesn't matter for txf

gk104/ir: sampler doesn't matter for txf

We actually leave the sampler unset for OP_TXF, which caused the GK104+
logic to treat some texel fetches as indirect. While this works, it's
incredibly wasteful. This only happened when the texture was > 0 (since
sampler remained == 0).

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "11.0 11.1" <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 63b850403c90f33c295d3ad6be4ad749d4ea6274)