dts: bindings: clock: renesas_ra: Change `_` to `-` in property name

`-` is preferred over `_` in devicetree property names.
Since, change `clk_src`, `clk_div`, and `clk_out_div` to
`clk-src`, `clk-div`, and `clk-out-div`.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>