staging: r8188eu: use mac_pton() in rtw_macaddr_cfg()

Instead of a custom approach use mac_pton() to convert the mac
address string. With mac_pton() the driver also validates the
input now.

Signed-off-by: Michael Straube <straube.linux@gmail.com>
Link: https://lore.kernel.org/r/20210830121508.6411-2-straube.linux@gmail.com


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