ath5k: fix building with LEDS=m

Randconfig builds still show a failure for the ath5k driver,
similar to the one that was fixed for ath9k earlier:

WARNING: unmet direct dependencies detected for MAC80211_LEDS
  Depends on [n]: NET [=y] && WIRELESS [=y] && MAC80211 [=y] && (LEDS_CLASS [=m]=y || LEDS_CLASS [=m]=MAC80211 [=y])
  Selected by [m]:
  - ATH5K [=m] && NETDEVICES [=y] && WLAN [=y] && WLAN_VENDOR_ATH [=y] && (PCI [=y] || ATH25) && MAC80211 [=y]
net/mac80211/led.c: In function 'ieee80211_alloc_led_names':
net/mac80211/led.c:34:22: error: 'struct led_trigger' has no member named 'name'
   34 |         local->rx_led.name = kasprintf(GFP_KERNEL, "%srx",
      |                      ^

Copying the same logic from my ath9k patch makes this one work
as well, stubbing out the calls to the LED subsystem.

Fixes: b64acb28 ("ath9k: fix build error with LEDS_CLASS=m")
Fixes: 72cdab80 ("ath9k: Do not select MAC80211_LEDS by default")
Fixes: 3a078876

 ("ath5k: convert LED code to use mac80211 triggers")
Link: https://lore.kernel.org/all/20210722105501.1000781-1-arnd@kernel.org/
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210920122359.353810-1-arnd@kernel.org