nir: Make lower_wpos_ytransform_block a void function.

The return value was used for the old nir_foreach_block callback system,
but at this point it no longer means anything.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Rob Clark <robdclark@gmail.com>

src/compiler/nir/nir_lower_wpos_ytransform.c

@@ -276,7 +276,7 @@ lower_interp_var_at_offset(lower_wpos_ytransform_state *state,
                                                      flip_y)));
 }
 
-static bool
+static void
 lower_wpos_ytransform_block(lower_wpos_ytransform_state *state, nir_block *block)
 {
    nir_foreach_instr_safe(instr, block) {
@@ -301,8 +301,6 @@ lower_wpos_ytransform_block(lower_wpos_ytransform_state *state, nir_block *block
             lower_fddy(state, alu);
       }
    }
-
-   return true;
 }
 
 static void