staging: rtl8723au: use %pM and %ph formatting

use %pM and %ph specifiers instead of placing each byte on stack.
(staging/rtl8723au/TODO)

Signed-off-by: Daniil Leshchev <meleodr@gmail.com>
Acked-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>