nvmem: qfprom: Mark core clk as optional

nvmem: qfprom: Mark core clk as optional

On some platforms like sc7280 on non-ChromeOS devices the core clock
cannot be touched by Linux so we cannot provide it. Mark it as optional
as accessing qfprom for reading works without it but we still prohibit
writing if we cannot provide the clock.

Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20231020105545.216052-2-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>