[libc][time] Ensure the data types are consistent

components/drivers/src/ringbuffer.c

@@ -244,7 +244,7 @@ rt_size_t rt_ringbuffer_peak(struct rt_ringbuffer *rb, rt_uint8_t **ptr)
 
     *ptr = &rb->buffer_ptr[rb->read_index];
 
-    if(rb->buffer_size - rb->read_index > size)
+    if((rt_size_t)(rb->buffer_size - rb->read_index) > size)
     {
         rb->read_index += size;
         return size;

components/libc/compilers/common/time.c

@@ -240,7 +240,7 @@ RTM_EXPORT(mktime);
 char* asctime_r(const struct tm *t, char *buf)
 {
     /* Checking input validity */
-    if (rt_strlen(days) <= (t->tm_wday << 2) || rt_strlen(months) <= (t->tm_mon << 2))
+    if ((int)rt_strlen(days) <= (t->tm_wday << 2) || (int)rt_strlen(months) <= (t->tm_mon << 2))
     {
         LOG_W("asctime_r: the input parameters exceeded the limit, please check it.");
         *(int*) buf = *(int*) days;