net: ethernet: mac89x0: add missing MODULE_DESCRIPTION() macro

net: ethernet: mac89x0: add missing MODULE_DESCRIPTION() macro

With ARCH=m68k, make allmodconfig && make W=1 C=1 reports:
WARNING: modpost: missing MODULE_DESCRIPTION() in drivers/net/ethernet/cirrus/mac89x0.o

Add the missing invocation of the MODULE_DESCRIPTION() macro.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://lore.kernel.org/r/20240618-md-m68k-drivers-net-ethernet-cirrus-v1-1-07f5bd0b64cb@quicinc.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>