brcmsmac: Fix build dep on LEDS_CLASS

brcmsmac: Fix build dep on LEDS_CLASS

When building randconfigs with CONFIG_BCMA_DRIVER_GPIO=y, I get

drivers/built-in.o: In function `brcms_led_unregister':
(.text+0x351aca): undefined reference to `led_classdev_unregister'
drivers/built-in.o: In function `brcms_led_register':
(.text+0x351c65): undefined reference to `led_classdev_register'

during final linking stage because brcmsmac/led.c needs LEDS_CLASS for
registering/deregistering the led device. Select the required symbols.

Cc: Arend van Spriel <arend@broadcom.com>
Cc: "Rafał Miłecki" <zajec5@gmail.com>
Cc: <linux-wireless@vger.kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>