freedreno/ir3: fix setup_input for sparse vertex inputs

freedreno/ir3: fix setup_input for sparse vertex inputs

With turnip we can have sparse input variables like:

decl_var shader_in INTERP_MODE_NONE float @1 (VERT_ATTRIB_GENERIC1.x, 1, 0)
decl_var shader_in INTERP_MODE_NONE float @2 (VERT_ATTRIB_GENERIC1.y, 1, 0)
decl_var shader_in INTERP_MODE_NONE float @3 (VERT_ATTRIB_GENERIC1.w, 1, 0)

Example of a test fixed:

dEQP-VK.glsl.440.linkage.varying.component.vert_in.vec2.as_float_float_unused

Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5818>