dt-bindings: phy: mediatek,tphy: allow simple nodename pattern

The pattern for the nodename only allows t-phy@... , however, for the case
when the t-phy has no `reg` and only `ranges` (basically when the t-phy
is just a parent node), dtc will throw this warning:

Warning (unit_address_vs_reg): /t-phy@1a243000: node has a unit name, but no reg or ranges property

For a node like this:

sata_phy: t-phy@1a243000 {
ranges;

sata_port: sata-phy@1a243000 {
reg = <0 0x1a243000 0 0x0100>;
};
};

it is normal that the parent node 't-phy' would be without any address, as in:

sata_phy: t-phy {
ranges;

sata_port: sata-phy@1a243000 {
reg = <0 0x1a243000 0 0x0100>;
};
};

because being just a holder it does not have its own reg.

However the binding does not allow such a name for the t-phy, so with this
patch, making the `@[0-9a-f]+` part optional, such node is possible.

Signed-off-by: Eugen Hristev <eugen.hristev@collabora.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230814093931.9298-1-eugen.hristev@collabora.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>