net: amlogic,meson-dwmac: Fix "amlogic,tx-delay-ns" schema

The "amlogic,tx-delay-ns" property schema has unnecessary type reference
as it's a standard unit suffix, and the constraints are in freeform
text rather than schema.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Link: https://patch.msgid.link/20240909172342.487675-2-robh@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>