nir: Switch the arguments to nir_foreach_phi_src

This matches the "foreach x in container" pattern found in many other
programming languages.  Generated by the following regular expression:

s/nir_foreach_phi_src(\([^,]*\),\s*\([^,]*\))/nir_foreach_phi_src(\2, \1)/

and a similar expression for nir_foreach_phi_src_safe.

Reviewed-by: Eduardo Lima Mitev <elima@igalia.com>

src/compiler/nir/nir_opt_dead_cf.c

@@ -97,7 +97,7 @@ opt_constant_if(nir_if *if_stmt, bool condition)
 
       nir_phi_instr *phi = nir_instr_as_phi(instr);
       nir_ssa_def *def = NULL;
-      nir_foreach_phi_src(phi, phi_src) {
+      nir_foreach_phi_src(phi_src, phi) {
          if (phi_src->pred != last_block)
             continue;