staging/rtl8723au: Use %pM format specifier to print mac address

printk() supports %pM format specifier for printing 6-byte MAC/FDDI
addresses in hex notation small buffers, let's use it intead of %x:%x...

Signed-off-by: Alexander Kuleshov <kuleshovmail@gmail.com>
Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>