ppir has some code that operates on all ppir_src variables, and for that
uses ppir_node_get_src.
lod bias support introduced a separate ppir_src that is inaccessible by
that function, causing it to be missed by the compiler in some routines.
Ultimately this caused, in some cases, a bug in const lowering:

  .../pp/lower.c:42: ppir_lower_const: Assertion `src != NULL' failed.

This fix moves the ppir_srcs in ppir_load_texture_node together so they
don't get missed.

Fixes: 721d82cf

 lima/ppir: add lod-bias support

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Reviewed-by: Vasily Khoruzhick <anarsoul@gmail.com>
Tested-by: Marge Bot <mesa/mesa!3185>
Part-of: <mesa/mesa!3185>