riscv: Fix esprv_intc_int_set_threshold() naming

This commit fixes the function declaration naming from esprv_intc_set_threshold()
to esprv_intc_int_set_threshold(), thus allowing the underlying ROM funciton to be
exposed via the header.

components/freertos/FreeRTOS-Kernel/portable/riscv/port.c

@@ -88,7 +88,6 @@ StackType_t *xIsrStackTop = &xIsrStack[0] + (configISR_STACK_SIZE & (~((portPOIN
 
 // ----------------- Scheduler Start/End -------------------
 
-extern void esprv_intc_int_set_threshold(int); // FIXME, this function is in ROM only
 BaseType_t xPortStartScheduler(void)
 {
     uxInterruptNesting = 0;