Improve const correctness.

See https://usfirst.collab.net/sf/tracker/do/viewArtifact/projects.wpilib/tracker.4_defects/artf4148

Change-Id: I47b0d5a91fd49e47e2c7348b0705e998ec815682

wpilibc/wpilibC++Devices/src/VictorSP.cpp

@@ -65,7 +65,7 @@ void VictorSP::Set(float speed, uint8_t syncGroup)
  *
  * @return The most recently set value for the PWM between -1.0 and 1.0.
  */
-float VictorSP::Get()
+float VictorSP::Get() const
 {
 	return GetSpeed();
 }