MAINTAINERS: adjust file entry for of_net.c after movement

Commit e330fb14 ("of: net: move of_net under net/") moves of_net.c
to ./net/core/, but misses to adjust the reference to this file in
MAINTAINERS.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains:

   warning: no file matches    F:    drivers/of/of_net.c

Adjust the file entry after this file movement.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20211016055815.14397-1-lukas.bulwahn@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

MAINTAINERS

@@ -7012,7 +7012,6 @@ F:	drivers/net/mdio/fwnode_mdio.c
 F:	drivers/net/mdio/of_mdio.c
 F:	drivers/net/pcs/
 F:	drivers/net/phy/
-F:	drivers/of/of_net.c
 F:	include/dt-bindings/net/qca-ar803x.h
 F:	include/linux/*mdio*.h
 F:	include/linux/mdio/*.h
@@ -7024,6 +7023,7 @@ F:	include/linux/platform_data/mdio-gpio.h
 F:	include/trace/events/mdio.h
 F:	include/uapi/linux/mdio.h
 F:	include/uapi/linux/mii.h
+F:	net/core/of_net.c
 
 EXFAT FILE SYSTEM
 M:	Namjae Jeon <linkinjeon@kernel.org>