nir: Remove spurious return from void function.

Left over from 450c061362.

Trivial.  Built locally with clang and gcc.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95296

src/compiler/nir/nir_lower_double_packing.c

@@ -75,8 +75,6 @@ lower_double_pack_impl(nir_function_impl *impl)
          nir_instr_remove(&alu_instr->instr);
       }
    }
-
-   return true;
 }
 
 void