SITL: Gripper_EPM compiler warning resolved by using float and fabsf

libraries/SITL/SIM_Gripper_EPM.cpp

@@ -107,7 +107,7 @@ bool Gripper_EPM::should_report()
         return false;
     }
 
-    if (abs(reported_field_strength - field_strength) > 10.0) {
+    if (fabsf(reported_field_strength - field_strength) > 10.0) {
         return true;
     }
 

libraries/SITL/SIM_Gripper_EPM.h

@@ -48,8 +48,8 @@ private:
 
     bool servo_based = true;
 
-    double field_strength; // percentage
+    float field_strength;   // percentage
-    double reported_field_strength = -1; // unlikely
+    float reported_field_strength = -1; // unlikely
 
     // I've a feeling these are probably a higher order than this:
     const float field_strength_slew_rate = 400; // (percentage of delta between field strength and 100)/second