cpufreq: apple-soc: Set fallback transition latency to APPLE_DVFS_TRANSITION_TIMEOUT

The driver already assumes transitions will not take longer than
APPLE_DVFS_TRANSITION_TIMEOUT in apple_soc_cpufreq_set_target(), so it
makes little sense to set CPUFREQ_ETERNAL as the transition latency
when the transistion latency is not given by the opp-table.

Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Nick Chan <towinchenmi@gmail.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>