sched/getpid: replace syscall getpid/tid/ppid() to kernel version

NuttX kernel should not use the syscall functions, especially after
enabling CONFIG_SCHED_INSTRUMENTATION_SYSCALL, all system functions
will be traced to backend, which will impact system performance.

Signed-off-by: chao an <anchao@xiaomi.com>

sched/mqueue/mq_timedreceive.c

@@ -202,7 +202,8 @@ ssize_t file_mq_timedreceive(FAR struct file *mq, FAR char *msg,
 
       /* Start the watchdog */
 
-      wd_start(&rtcb->waitdog, ticks, nxmq_rcvtimeout, gettid());
+      wd_start(&rtcb->waitdog, ticks,
+               nxmq_rcvtimeout, nxsched_gettid());
     }
 
   /* Get the message from the message queue */

sched/mqueue/mq_timedsend.c

@@ -245,7 +245,7 @@ int file_mq_timedsend(FAR struct file *mq, FAR const char *msg,
 
   /* Start the watchdog and begin the wait for MQ not full */
 
-  wd_start(&rtcb->waitdog, ticks, nxmq_sndtimeout, gettid());
+  wd_start(&rtcb->waitdog, ticks, nxmq_sndtimeout, nxsched_gettid());
 
   /* And wait for the message queue to be non-empty */