freerots: fix rtos_int_exit writing outside ISR stack
rtos_int_exit would store RA at an offset of 4 byte from the SP,
where the offset should be 0.
This caused rtos_int_exit to overwrite variables in bss.
@@ -90,9 +90,9 @@ isr_skip_decrement:
/* preserve return address and schedule next task */
addi sp,sp,-4
- sw ra, 0x04(sp)
+ sw ra, 0(sp)
call vTaskSwitchContext
- lw ra, 0x04(sp)
+ lw ra, 0(sp)
addi sp, sp, 4
/* Clears the switch pending flag */
