ath9k_htc: Do not select MAC80211_LEDS by default

The ath9k_htc driver hides all LEDs related code behind
CONFIG_MAC80211_LEDS ifdefs so it does not really require the
MAC80211_LEDS.  The code builds and works just 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/20200820120444.8809-1-krzk@kernel.org