ARM: dts: r7s9210: Remove bogus clock-names from OSTM nodes

Usually it does not hurt to add "clock-names" properties, even if the
(pre-json-schema) DT bindings do not mention them.

However, the actual clock names for the OS Timer nodes are not fixed,
but contain the indices of the consumer instances.  Hence they cannot
easily be used by a driver, without scanning for all possible indices.

Remove them, as the OSTM DT bindings do not specify clock-names anyway.

Fixes: bbbcd02b ("ARM: dts: r7s9210: Initial SoC device tree")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Chris Brandt <Chris.Brandt@renesas.com>
Link: https://lore.kernel.org/r/20200427192932.28967-1-geert+renesas@glider.be