xtesa: fix lost save & restore states caused by merge code

this is caused by:
35c8c80

Signed-off-by: ligd <liguiding1@xiaomi.com>

arch/xtensa/src/common/xtensa_switchcontext.c

@@ -59,7 +59,24 @@ void up_switch_context(struct tcb_s *tcb, struct tcb_s *rtcb)
 {
   /* Are we in an interrupt handler? */
 
-  if (!up_current_regs())
+  if (up_current_regs())
+    {
+      /* Yes, then we have to do things differently.
+       * Just copy the current_regs into the OLD rtcb.
+       */
+
+      xtensa_savestate(rtcb->xcp.regs);
+
+      /* Then switch contexts.  Any necessary address environment
+       * changes will be made when the interrupt returns.
+       */
+
+      xtensa_restorestate(tcb->xcp.regs);
+    }
+
+  /* No, then we will need to perform the user context switch */
+
+  else
     {
       /* Switch context to the context of the task at the head of the
        * ready to run list.