SH: cpuidle: remove CPUIDLE_DRIVER_STATE_START usage

The CPUIDLE_DRIVER_STATE_START constant is only set when the kernel compilation
option CONFIG_ARCH_HAS_CPU_RELAX is set, but this is only relatated to x86, so
it is always zero.

Remove the reference to this constant in the code.

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>