brcmsmac: add support for BCM43224 with PCI id of 14e4:a8d8

This device can be found on some embedded devices connected to a
Broadcom SoC like the BCM4718.
I tested this with my Netgear WNDR3400 v1.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>