MAINTAINERS: Update X-Gene SoC ethernet maintainer

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: Keyur Chudgar <kchudgar@apm.com>
Signed-off-by: Quan Nguyen <qnguyen@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -896,6 +896,7 @@ F:	arch/arm64/boot/dts/apm/
 APPLIED MICRO (APM) X-GENE SOC ETHERNET DRIVER
 M:	Iyappan Subramanian <isubramanian@apm.com>
 M:	Keyur Chudgar <kchudgar@apm.com>
+M:	Quan Nguyen <qnguyen@apm.com>
 S:	Supported
 F:	drivers/net/ethernet/apm/xgene/
 F:	drivers/net/phy/mdio-xgene.c