clk: renesas: rcar-usb2-clock-sel: Fix error handling in .probe()

The error handling paths after pm_runtime_get_sync() have no refcount
decrement, which leads to refcount leak.

Signed-off-by: Dinghao Liu <dinghao.liu@zju.edu.cn>
Link: https://lore.kernel.org/r/20210415073338.22287-1-dinghao.liu@zju.edu.cn


[geert: Remove now unused variable priv]
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>