nir: fix unpack_64_4x16 in lower_alu_to_scalar()

Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Reviewed-By: Timur Kristóf <timur.kristof@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4002>

src/compiler/nir/nir_lower_alu_to_scalar.c

@@ -208,6 +208,7 @@ lower_alu_instr_scalar(nir_builder *b, nir_instr *instr, void *_data)
    }
 
    case nir_op_unpack_64_2x32:
+   case nir_op_unpack_64_4x16:
    case nir_op_unpack_32_2x16:
       return NULL;