watchdog: pcwd_usb: Fix attempting to access uninitialized memory

The stack variable msb and lsb may be used uninitialized in function
usb_pcwd_get_temperature and usb_pcwd_get_timeleft when usb card no response.

The build waring is:
drivers/watchdog/pcwd_usb.c:336:22: error: ‘lsb’ is used uninitialized in this function [-Werror=uninitialized]
  *temperature = (lsb * 9 / 5) + 32;
                  ~~~~^~~
drivers/watchdog/pcwd_usb.c:328:21: note: ‘lsb’ was declared here
  unsigned char msb, lsb;
                     ^~~
cc1: all warnings being treated as errors
scripts/Makefile.build:250: recipe for target 'drivers/watchdog/pcwd_usb.o' failed
make[3]: *** [drivers/watchdog/pcwd_usb.o] Error 1

Fixes: b7e04f8c ("mv watchdog tree under drivers")
Signed-off-by: Li Hua <hucool.lihua@huawei.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20221116020706.70847-1-hucool.lihua@huawei.comSigned-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>

drivers/watchdog/pcwd_usb.c

@@ -325,7 +325,8 @@ static int usb_pcwd_set_heartbeat(struct usb_pcwd_private *usb_pcwd, int t)
 static int usb_pcwd_get_temperature(struct usb_pcwd_private *usb_pcwd,
 							int *temperature)
 {
-	unsigned char msb, lsb;
+	unsigned char msb = 0x00;
+	unsigned char lsb = 0x00;
 
 	usb_pcwd_send_command(usb_pcwd, CMD_READ_TEMP, &msb, &lsb);
 
@@ -341,7 +342,8 @@ static int usb_pcwd_get_temperature(struct usb_pcwd_private *usb_pcwd,
 static int usb_pcwd_get_timeleft(struct usb_pcwd_private *usb_pcwd,
 								int *time_left)
 {
-	unsigned char msb, lsb;
+	unsigned char msb = 0x00;
+	unsigned char lsb = 0x00;
 
 	/* Read the time that's left before rebooting */
 	/* Note: if the board is not yet armed then we will read 0xFFFF */