change time from double to struct timespec

LibSidServo/PID.h

@@ -27,7 +27,7 @@ typedef struct {
     double prev_error;  // Previous error
     double integral;    // Integral term
     double *pidIarray;  // array for Integral
-    double prevT;       // time of previous correction
+    struct timespec prevT; // time of previous correction
     size_t pidIarrSize; // it's size
     size_t curIidx;     // and index of current element
 } PIDController_t;