clk: scmi: Add duty cycle ops only when duty cycle is supported

For some of the SCMI based platforms, the oem extended config may be
supported, but not for duty cycle purpose. Skip the duty cycle ops if
err return when trying to get duty cycle info.

Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>