nir/spirv: fix build_mat_subdet stack smasher
nir/spirv: fix build_mat_subdet stack smasher

The sub-determinate implementation pattern fixed by
6a7e2904e0a2a6f8efbf739a1b3cad7e1e4ab42d has a second instance in the
same file.

With the previous algorithm, when row and j are both 3, the index
overruns the array.  This only impacts the stack on 32 bit builds.

Reviewed-by: Jason Ekstrand <b186559eaedf698788888c8a2559b4efb4db10d6@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler