microsoft/compiler: dxil_nir_opt_alu_deref_srcs: return progress

dxil_nir_opt_alu_deref_srcs will always return false because
the progress variable is declared both for the function and also
inside the loop.

Spotted by a unused-but-set-variable warning from clang

Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14290>

src/microsoft/compiler/dxil_nir.c

@@ -934,7 +934,6 @@ dxil_nir_opt_alu_deref_srcs(nir_shader *nir)
          continue;
       assert(func->impl);
 
-      bool progress = false;
       nir_builder b;
       nir_builder_init(&b, func->impl);