MAINTAINERS: adjust file entry for of_net.c after movement

MAINTAINERS: adjust file entry for of_net.c after movement

BugLink: https://bugs.launchpad.net/bugs/1964361
commit f616447034a120b18f6e612814641e7d8f5d7f0a upstream.

Commit e330fb14590c ("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.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>