Documentation: RIEBL_MAGIC isn't a magic number

At least not in the sense described in magic-number.rst:
it determines whether the Atari VME Lance Ethernet card has a hardware
MAC address or not, and is set thereby to indicate this

Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Link: https://lore.kernel.org/r/773e5a8fe80201bed0dff5cdb1ce6f4272b0cc92.1663280877.git.nabijaczleweli@nabijaczleweli.xyz


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