net: wireless: iwlegacy: fix build error for il_pm_ops

Fix build error for il_pm_ops if CONFIG_PM is set
but CONFIG_PM_SLEEP is not set.

ERROR: "il_pm_ops" [drivers/net/wireless/iwlegacy/iwl4965.ko] undefined!
ERROR: "il_pm_ops" [drivers/net/wireless/iwlegacy/iwl3945.ko] undefined!
make[1]: *** [__modpost] Error 1
make: *** [modules] Error 2

Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Cc: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: "John W. Linville" <linville@tuxdriver.com>
Cc: netdev@vger.kernel.org
Cc: linux-wireless@vger.kernel.org
Cc: Jingoo Han <jg1.han@samsung.com>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>