freedreno/ir3/ra: fix pre-color edge case

freedreno/ir3/ra: fix pre-color edge case

Fixes a case where you have something like:

   aVecOutput.z = aScalarInput;

In particular, skipping over things that are not the first component is
wrong.. in the above case the input we need to precolor is the 3rd
component.  But we need to adjust the target register according to the
offset.

Fixes android.hardware.nativehardware.cts.AHardwareBufferNativeTests

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5601>