staging: rtl8723bs: ignore unused wiphy_wowlan object warnings

The wake-on-wlan stub is unused when the device power management
functionality is disabled in the kernel, creating a warning when
building the driver.

drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c:50:42: warning: ‘wowlan_stub’ defined but not used [-Wunused-const-variable=]

Add the __maybe_unused annotation to silence this warning.
Signed-off-by: Bryan Brattlof <hello@bryanbrattlof.com>
Link: https://lore.kernel.org/r/20210916231928.2021584-1-hello@bryanbrattlof.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/os_dep/ioctl_cfg80211.c

@@ -47,7 +47,7 @@ static const u32 rtw_cipher_suites[] = {
  * Moreover wowlan has to be enabled via a the nl80211_set_wowlan callback.
  * (from user space, e.g. iw phy0 wowlan enable)
  */
-static const struct wiphy_wowlan_support wowlan_stub = {
+static __maybe_unused const struct wiphy_wowlan_support wowlan_stub = {
 	.flags = WIPHY_WOWLAN_ANY,
 	.n_patterns = 0,
 	.pattern_max_len = 0,