cpufreq: scmi: Fix an error message

'ret' is known to be 0 here.
The last error code is stored in 'nr_opp', so use it in the error message.

Fixes: 71a37cd6 ("scmi-cpufreq: Remove deferred probe")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>