misc: flush syslog before possible long time cost coredump

When coredump to mtd, it maybe cost lots of time, do flush syslog can
make user access all log when coredump processing, should be better.

Signed-off-by: buxiasen <buxiasen@xiaomi.com>

sched/misc/assert.c

@@ -742,7 +742,12 @@ static void dump_fatal_info(FAR struct tcb_s *rtcb,
 
 #if defined(CONFIG_BOARD_COREDUMP_SYSLOG) || \
     defined(CONFIG_BOARD_COREDUMP_BLKDEV)
-      /* Dump core information */
+
+  /* Flush previous SYSLOG data before possible long time coredump */
+
+  syslog_flush();
+
+  /* Dump core information */
 
 #  ifdef CONFIG_BOARD_COREDUMP_FULL
   coredump_dump(INVALID_PROCESS_ID);