staging: r8188eu: replace MACADDRLEN with ETH_ALEN

Replace the custom constant MACADDRLEN with in-kernel ETH_ALEN.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20211009104419.8811-2-straube.linux@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>