mac80211: don't open-code LED manipulations

We shouldn't open-code led_trigger_blink() or led_trigger_event(),
use them instead of badly open-coding them. This also fixes the
locking, led_trigger_blink() and led_trigger_event() now use
read_lock_irqsave().

Link: https://lore.kernel.org/r/20210616212804.b19ba1c60353.I8ea1b4defd5e12fc20ef281291e602feeec336a6@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>