drm/amdgpu: Fix uninitialized variable warning in amdgpu_afmt_acr

Assign value to clock to fix the warning below:
"Using uninitialized value res. Field res.clock is uninitialized"

Signed-off-by: Ma Jun <Jun.Ma2@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>