arm64: dts: intel: socfpga: override clocks by label

Using full paths to extend or override a device tree node is error
prone.  If there was a typo error, a new node will be created instead of
extending the existing node.  This will lead to run-time errors that
could be hard to detect.

A mistyped label on the other hand, will cause a dtc compile error
(during build time).

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>