SH: cpuidle: remove pointless initialization

The driver is a global static variable automatically initialized to zero.

Removing the useless initialization in the init function.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>