freedreno/ir3: fix input ncomp for vertex shaders

ncomp is never set for vertex shaders, but a3xx and a4xx still use it.

Fixes: 831f1a05 freedreno/ir3: rework varying packing

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Reviewed-by: Rob Clark <robdclark@chromium.org>
(cherry picked from commit 1db86d8b)