mfd: qcom-spmi-pmic: Switch to EXPORT_SYMBOL_GPL()

Switch to using EXPORT_SYMBOL_GPL() for the revid helper as there is no
reason not to use it.

Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Acked-by: Caleb Connolly <caleb.connolly@linaro.org>
Link: https://lore.kernel.org/r/20231003152927.15000-4-johan+linaro@kernel.org


Signed-off-by: Lee Jones <lee@kernel.org>