v3dv: mark the right bit to swap R/B vertex attributes

Now that the R/B swap mask for vertex attributes handles all the
attributes, ensure the right generic vertex attribute is marked.

Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7196>
1 file changed