drm/amd/powerplay: fix dpm freq unit error (10KHz -> Mhz)

the interface smu_v11_0_get_current_clk_freq should be return 10Khz not
Mhz unit to adapt vega20 and navi10 asic at the same time.

Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>