leds: trigger: ledtrig-cpu: Fix incorrectly documented param 'ledevt'

Fixes the following W=1 kernel build warning(s):

 drivers/leds/trigger/ledtrig-cpu.c:52: warning: Function parameter or member 'ledevt' not described in 'ledtrig_cpu'
 drivers/leds/trigger/ledtrig-cpu.c:52: warning: Excess function parameter 'evt' description in 'ledtrig_cpu'

Cc: Pavel Machek <pavel@ucw.cz>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Bryan Wu <bryan.wu@canonical.com>
Cc: linux-leds@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>