drivers/syslog: Call up_puts instead up_putc one by one

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

drivers/syslog/syslog_channel.c

@@ -218,14 +218,9 @@ static ssize_t syslog_default_write(FAR struct syslog_channel_s *channel,
 {
 #if defined(CONFIG_ARCH_LOWPUTC)
   static sem_t sem = SEM_INITIALIZER(1);
-  size_t nwritten;
 
   nxsem_wait(&sem);
-  for (nwritten = 0; nwritten < buflen; nwritten++)
-    {
-      up_putc(buffer[nwritten]);
-    }
-
+  up_puts(buffer);
   nxsem_post(&sem);
 #endif