tty: synclink_cs: Use bitwise instead of arithmetic operator for flags

This silences the following coccinelle warning:
drivers/s390/char/tape_34xx.c:360:38-39: WARNING: sum of probable bitmasks, consider |

we will try to make code cleaner

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Haowen Bai <baihaowen@meizu.com>
Link: https://lore.kernel.org/r/1647846757-946-1-git-send-email-baihaowen@meizu.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>