reset: reset-scmi: add missing handle initialisation

scmi_reset_data->handle needs to be initialised at probe, so that it
can be later used to access scmi reset protocol APIs using the same.

Since it was tested with a module that obtained handle elsewhere,
it was missed easily. Add the missing scmi_reset_data->handle
initialisation to fix the issue.

Fixes: c8ae9c2d

 ("reset: Add support for resets provided by SCMI")
Acked-by: Philipp Zabel <p.zabel@pengutronix.de>
Reported-by: Etienne Carriere <etienne.carriere@linaro.org>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>