spmi: add a helper to look up an SPMI device from a device node

The helper function spmi_device_from_of() takes a device node and
returns the SPMI device associated with it.
This is like of_find_device_by_node but for SPMI devices.

Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lore.kernel.org/r/20220429220904.137297-2-caleb.connolly@linaro.org


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>