cpufreq: Documentation: Update description of rate_limit_us default value

cpufreq: Documentation: Update description of rate_limit_us default value

Due to commit 37c6dccd6837 ("cpufreq: Remove LATENCY_MULTIPLIER")
updating the acquisition logic of cpufreq_policy_transition_delay_us(),
the original description of 2 ms has become inaccurate.

Therefore, update the description of the default value for
rate_limit_us from 2ms to 1ms.

Signed-off-by: Yaxiong Tian <tianyaxiong@kylinos.cn>
[ rjw: Subject and changelog edits ]
Link: https://patch.msgid.link/20260203093501.1138721-1-tianyaxiong@kylinos.cn
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>