cpufreq: amd-pstate: Update policy->cur in amd_pstate_adjust_perf()

Driver should update policy->cur after updating the frequency.
Currently amd_pstate doesn't update policy->cur when `adjust_perf`
is used. Which causes /proc/cpuinfo to show wrong cpu frequency.
Fix this by updating policy->cur with correct frequency value in
adjust_perf function callback.

- Before the fix: (setting min freq to 1.5 MHz)

[root@amd]# cat /proc/cpuinfo | grep "cpu MHz" | sort | uniq --count
      1 cpu MHz         : 1777.016
      1 cpu MHz         : 1797.160
      1 cpu MHz         : 1797.270
    189 cpu MHz         : 400.000

- After the fix: (setting min freq to 1.5 MHz)

[root@amd]# cat /proc/cpuinfo | grep "cpu MHz" | sort | uniq --count
      1 cpu MHz         : 1753.353
      1 cpu MHz         : 1756.838
      1 cpu MHz         : 1776.466
      1 cpu MHz         : 1776.873
      1 cpu MHz         : 1777.308
      1 cpu MHz         : 1779.900
    183 cpu MHz         : 1805.231
      1 cpu MHz         : 1956.815
      1 cpu MHz         : 2246.203
      1 cpu MHz         : 2259.984

Fixes: 1d215f03 ("cpufreq: amd-pstate: Add fast switch function for AMD P-State")
Signed-off-by: Wyes Karny <wyes.karny@amd.com>
[ rjw: Subject edits ]
Cc: 5.17+ <stable@vger.kernel.org> # 5.17+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>