feat: Initialize local variables to prevent GCC compilation warnings

components/drivers/serial/dev_serial_v2.c

@@ -747,7 +747,7 @@ static rt_ssize_t _serial_fifo_tx_nonblocking(struct rt_device *dev,
 {
     struct rt_serial_device  *serial;
     struct rt_serial_tx_fifo *tx_fifo;
-    rt_uint8_t               *put_ptr;
+    rt_uint8_t               *put_ptr = RT_NULL;
     rt_base_t                 level;
     rt_size_t                 send_size;
     rt_ssize_t                transmit_size;

components/fal/src/fal_rtt.c

@@ -599,7 +599,7 @@ static void fal(rt_uint8_t argc, char **argv) {
     else
     {
         const char *operator = argv[1];
-        rt_uint32_t addr, size;
+        rt_uint32_t addr = 0, size = 0;
 
         if (!strcmp(operator, "probe"))
         {

components/utilities/ymodem/ymodem.c

@@ -204,7 +204,7 @@ static rt_err_t _rym_do_handshake(
     enum rym_code code;
     rt_size_t i;
     rt_uint16_t recv_crc, cal_crc;
-    rt_size_t data_sz;
+    rt_size_t data_sz = 0;
     rt_tick_t tick;
 
     ctx->stage = RYM_STAGE_ESTABLISHING;