thinkpad-acpi: fix sign of ERESTARTSYS return

The returned error should be negative
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: <stable@kernel.org>
Signed-off-by: Len Brown <len.brown@intel.com>

drivers/platform/x86/thinkpad_acpi.c

@@ -6313,7 +6313,7 @@ static int brightness_write(char *buf)
 	 * Doing it this way makes the syscall restartable in case of EINTR
 	 */
 	rc = brightness_set(level);
-	return (rc == -EINTR)? ERESTARTSYS : rc;
+	return (rc == -EINTR)? -ERESTARTSYS : rc;
 }
 
 static struct ibm_struct brightness_driver_data = {