watchdog: pcwd_usb: Use allocated buffer for usb_control_msg

usb_control_msg() must use a dma-capable buffer.

This fixes the following error reported by smatch:

drivers/watchdog/pcwd_usb.c:257 usb_pcwd_send_command() error: doing dma on the
stack (buf)
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>

drivers/watchdog/pcwd_usb.c

@@ -235,13 +235,17 @@ static int usb_pcwd_send_command(struct usb_pcwd_private *usb_pcwd,
 		unsigned char cmd, unsigned char *msb, unsigned char *lsb)
 {
 	int got_response, count;
-	unsigned char buf[6];
+	unsigned char *buf;
 
 	/* We will not send any commands if the USB PCWD device does
 	 * not exist */
 	if ((!usb_pcwd) || (!usb_pcwd->exists))
 		return -1;
 
+	buf = kmalloc(6, GFP_KERNEL);
+	if (buf == NULL)
+		return 0;
+
 	/* The USB PC Watchdog uses a 6 byte report format.
 	 * The board currently uses only 3 of the six bytes of the report. */
 	buf[0] = cmd;			/* Byte 0 = CMD */
@@ -277,6 +281,8 @@ static int usb_pcwd_send_command(struct usb_pcwd_private *usb_pcwd,
 		*lsb = usb_pcwd->cmd_data_lsb;
 	}
 
+	kfree(buf);
+
 	return got_response;
 }