cpufreq: Fix re-boost issue after hotplugging a CPU

It turns out that CPUX will stay on the base frequency after performing
these operations:

 1. boost all CPUs: echo 1 > /sys/devices/system/cpu/cpufreq/boost

 2. offline one CPU: echo 0 > /sys/devices/system/cpu/cpuX/online

 3. deboost all CPUs: echo 0 > /sys/devices/system/cpu/cpufreq/boost

 4. online CPUX: echo 1 > /sys/devices/system/cpu/cpuX/online

 5. boost all CPUs again: echo 1 > /sys/devices/system/cpu/cpufreq/boost

This is because max_freq_req of the policy is not updated during the
online process, and the value of max_freq_req before the last offline is
retained.

When the CPU is boosted again, freq_qos_update_request() will do nothing
because the old value is the same as the new one. This causes the CPU to
stay at the base frequency. Updating max_freq_req  in cpufreq_online()
will solve this problem.

Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://patch.msgid.link/20250117101457.1530653-2-zhenglifeng1@huawei.com


[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>