VHAL: fix CTS CarPropertyManagerTest#testRegisterCallback

This case asserts property PERF_VEHICLE_SPEED can have different
number event happened with different event rate:
SENSOR_RATE_NORMAL or SENSOR_RATE_FASTEST.
But CarPropertyManager.java says:
  Rate has no effect if the property has one of the following change modes
     *   CarPropertyConfig#VEHICLE_PROPERTY_CHANGE_MODE_STATIC
     *   CarPropertyConfig#VEHICLE_PROPERTY_CHANGE_MODE_ONCHANGE
So modify PERF_VEHICLE_SPEED change mode to CONTINUOUS.

Test:
run cts -m CtsCarTestCases -t android.car.cts.CarPropertyManagerTest#testRegisterCallback

Change-Id: I99e3d672d052a5cde9aaad78221caac510e81b40
Signed-off-by: Jindong <jindong.yue@nxp.com>