cpufreq: kryo: Fix possible error code dereference

In event of error returned by the nvmem_cell_read() non-pointer value
may be dereferenced. Fix this with error handling.
Additionally free the allocated speedbin buffer, as per the API.

Fixes: 9ce36edd1a52 (cpufreq: Add Kryo CPU scaling driver)
Signed-off-by: Ilia Lin <ilia.lin@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>