Input: sysrq - fix "stuck" SysRq mode

This shoud fix the problem with SysRq mode staying half-way enabled
and interfereing with normal PrtScrn operation after user presses ALT
for the first time.
Reported-and-tested-by: Éric Piel <E.A.B.Piel@tudelft.nl>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

drivers/char/sysrq.c

@@ -580,8 +580,12 @@ static bool sysrq_filter(struct input_handle *handle, unsigned int type,
 	case KEY_RIGHTALT:
 		if (value)
 			sysrq_alt = code;
-		else if (sysrq_down && code == sysrq_alt_use)
-			sysrq_down = false;
+		else {
+			if (sysrq_down && code == sysrq_alt_use)
+				sysrq_down = false;
+
+			sysrq_alt = 0;
+		}
 		break;
 
 	case KEY_SYSRQ: