MAINTAINERS: take maintainership of the cpmac Ethernet driver

This patch adds me as the maintainer of the CPMAC (AR7)
Ethernet driver.

Signed-off-by: Florian Fainelli <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

MAINTAINERS

···
 S:	Maintained
 F:	drivers/net/wan/cosa*
 
+CPMAC ETHERNET DRIVER
+P:	Florian Fainelli
+M:	[e-mail]
+L:	[e-mail]
+S:	Maintained
+F:	drivers/net/cpmac.c
+
 CPU FREQUENCY DRIVERS
 P:	Dave Jones
 M:	[e-mail]