The ADCINC14 has it's own ISR generated by PSoC Designer. The ISR has code that is necessary for the ADC to function correctly. So, creating your own ISR for the ADC is not the correct method. Instead, in the main loop, poll for the ADC data to be availabel and update the PWM period based on this value. Try the following code instead.
//Enable Global Interrupt
/*start the PWM16!*/
ADC_Result = ADCINC14_iGetDataClearFlag();
pwmValue = ADC_Result / 300;
PWM16_1_WritePulseWidth(pwmValue >> 1);