watchdog: f71808e_wdt: Fix magic close handling

BugLink: https://bugs.launchpad.net/bugs/1775771

[ Upstream commit 7bd3e7b7 ]

Watchdog close is "expected" when any byte is 'V' not just the last one.
Writing "V" to the device fails because the last byte is the end of string.

$ echo V > /dev/watchdog
f71808e_wdt: Unexpected close, not stopping watchdog!
Signed-off-by: Igor Pylypiv <igor.pylypiv@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/watchdog/f71808e_wdt.c

@@ -520,7 +520,8 @@ static ssize_t watchdog_write(struct file *file, const char __user *buf,
 				char c;
 				if (get_user(c, buf + i))
 					return -EFAULT;
-				expect_close = (c == 'V');
+				if (c == 'V')
+					expect_close = true;
 			}
 
 			/* Properly order writes across fork()ed processes */