MAINTAINERS: add maintainer for SFF/SFP/SFP+ support

Add maintainer entry for SFF/SFP/SFP+ support.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>