Ramps do not update device mapping

[THuckemann]

After changing the mapping of a devices parameter, the device has to be "updated" once for the parameter to work. This automatically done upon setting or getting a parameter, but apparently not, when device.param.ramp() is used.
As a result, the parameter appears not to be mapped resulting in a confusing error.

Until I fixed this properly, one can simply get all parameters once (e.g. with device.voltages())