staging: r8188eu: use ETH_ALEN

Use ETH_ALEN instead of hard-coding the value for the mac_addr buffer
in struct eeprom_priv.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210830121508.6411-4-straube.linux@gmail.com


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