[PATCH] watchdog: pcwd_usb: Fix attempting to access uninitialized memory

[Li Hua <hucool.lihua@xxxxxxxxxx>]

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: b7e04f8c61a4 ("mv watchdog tree under drivers")
Signed-off-by: Li Hua <hucool.lihua@xxxxxxxxxx>
---
 drivers/watchdog/pcwd_usb.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/watchdog/pcwd_usb.c b/drivers/watchdog/pcwd_usb.c
index 1bdaf17c1d38..89b0b5d8a7e6 100644
--- a/drivers/watchdog/pcwd_usb.c
+++ b/drivers/watchdog/pcwd_usb.c
@@ -326,8 +326,13 @@ static int usb_pcwd_get_temperature(struct usb_pcwd_private *usb_pcwd,
 							int *temperature)
 {
 	unsigned char msb, lsb;
+	int retval;
 
-	usb_pcwd_send_command(usb_pcwd, CMD_READ_TEMP, &msb, &lsb);
+	retval = usb_pcwd_send_command(usb_pcwd, CMD_READ_TEMP, &msb, &lsb);
+	if (retval != 1) {
+		pr_err("Card did not acknowledge CMD_READ_TEMP\n");
+		return -1;
+	}
 
 	/*
 	 * Convert celsius to fahrenheit, since this was
@@ -342,10 +347,16 @@ static int usb_pcwd_get_timeleft(struct usb_pcwd_private *usb_pcwd,
 								int *time_left)
 {
 	unsigned char msb, lsb;
+	int retval;
 
 	/* Read the time that's left before rebooting */
 	/* Note: if the board is not yet armed then we will read 0xFFFF */
-	usb_pcwd_send_command(usb_pcwd, CMD_READ_WATCHDOG_TIMEOUT, &msb, &lsb);
+	retval = usb_pcwd_send_command(usb_pcwd, CMD_READ_WATCHDOG_TIMEOUT,
+				&msb, &lsb);
+	if (retval != 1) {
+		pr_err("Card did not acknowledge CMD_READ_WATCHDOG_TIMEOUT\n");
+		return -1;
+	}
 
 	*time_left = (msb << 8) + lsb;
 
-- 
2.17.1