MAINTAINERS: remove Guvenc Gulce as net/smc maintainer

Remove myself as net/smc maintainer, as I am
leaving IBM soon and can not maintain net/smc anymore.

Cc: Julian Wiedmann <jwi@linux.ibm.com>
Acked-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Guvenc Gulce <guvenc@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>