nir: Fix broken fsat recognizer.
nir: Fix broken fsat recognizer.

We've probably never seen this ridiculous pattern in the wild, so it
didn't matter.

Reviewed-by: Connor Abbott <71178acffcc112b21e5858656e5751f5e4aa9364@gmail.com>
Reviewed-by: Jason Ekstrand <b186559eaedf698788888c8a2559b4efb4db10d6@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler