net: phy: sfp-bus.c: get rid of docs warnings

The indentation for the returned values are weird, causing those
warnings:

	./drivers/net/phy/sfp-bus.c:579: WARNING: Unexpected indentation.
	./drivers/net/phy/sfp-bus.c:619: WARNING: Unexpected indentation.

Use a list and change the identation for it to be properly
parsed by the documentation toolchain.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>