ath9k: Do not select MAC80211_LEDS by default

The ath9k driver hides all LEDs related code behind CONFIG_MAC80211_LEDS
ifdefs so it does not really require the MAC80211_LEDS.  The code builds
fine.  Convert the "select" into "imply" to allow disabling LED trigger
when not needed.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200820194049.28055-1-krzk@kernel.org