Call amdgpu_present_set_screen_vrr from amdgpu_vrr_property_update

If the window is currently flipping.

This might make a difference when the property gets disabled: Variable
refresh will now be disabled immediately in that case, instead of only
when the window can no longer use page flipping at all.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>