MAINTAINERS: SXGBE authors update

The mail address for Siva Reddy Kallam is bouncing, remove the email
address from the MAINTAINERS entry for Samsung's SXGBE driver.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>