MAINTAINERS: add dwmac-rk glue driver to the main Rockchip entry

MAINTAINERS: add dwmac-rk glue driver to the main Rockchip entry

The dwmac-rk glue driver is currently not caught by the general maintainer
entry for Rockchip SoCs, so add it explicitly, similar to the i2c driver.

The binding document in net/rockchip-dwmac.yaml already gets caught by
the wildcard match.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20251023111213.298860-6-heiko@sntech.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>