or1k: fix wrong masking of incoming in_status byte

In some circumstances this can lead to an misinterpreted
unknown status:

Error:  debug IF command write: Unknown status (-1304293920)
Error:  debug IF command write: Unknown status (-1304293920)
Error:  debug IF command write: Unknown status (158502000)

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>