cpufreq: userspace: make scaling_setspeed return the actual requested frequency

cpufreq: userspace: make scaling_setspeed return the actual requested frequency

According to the Linux kernel ABI documentation for 'scaling_setspeed':
  "It returns the last frequency requested by the governor (in kHz) or
   can be written to in order to set a new frequency for the policy."

However, the current implementation of show_speed() returns 'policy->cur'.
'policy->cur' represents the frequency after the driver has
resolved the request against the hardware frequency table and applied
policy limits (min/max).

This creates a discrepancy between the documentation/user expectation
and the actual code behavior. For instance:

 1. User writes a value to 'scaling_setspeed' that is not in the OPP
    table (e.g., user asks for A, driver rounds it to B).
 2. User reads 'scaling_setspeed'.
 3. Code returns B ('policy->cur').
 4. User expects A (the "frequency requested"), but gets B.

This patch changes show_speed() to return 'userspace->setspeed', which
stores the actual value last requested by the user. This restores the
read/write symmetry of the attribute and aligns the code with the ABI
description.

The effective frequency can still be observed via 'scaling_cur_freq' or
'cpuinfo_cur_freq', preserving the distinction between "what was
requested" (setspeed) and "what is effective" (cur_freq).

Signed-off-by: Pengjie Zhang <zhangpengjie2@huawei.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: lihuisong@huawei.com
Link: https://patch.msgid.link/20260116094623.2980031-1-zhangpengjie2@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>