dt-bindings: net: rename the bindings document for MediaTek STAR EMAC

The driver itself was renamed before getting merged into mainline, but
the binding document kept the old name. This makes both names consistent.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>