wireless: airo: re-use mac_pton()

mac_pton() converts 6-byte MAC / BSSID to binary format. Change an open coded
variant by the generic one.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>