Hi @DHARSAN
Based on error messages,

Your previous declaration of "FLEXCOMM2_DriverIRQHandler" with type void(void)
So you should the declaration of "FLEXCOMM2_DriverIRQHandler" with void FLEXCOMM2_DriverIRQHandler(USART_Type *base, usart_handle_t *handle);
Hope this will help you.
BR
Hang