nvc0/ir: fix emission of IMAD with NEG modifiers

The emitter tried to emit sub instead of subr when src0 has
actually a NEG modifier.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "11.0 12.0 13.0" <mesa-stable@lists.freedesktop.org>
2 files changed