escc: fix STATUS_SYNC bit in R_STATUS register

escc: fix STATUS_SYNC bit in R_STATUS register

After an SDLC "Enter hunt" command has been sent the STATUS_SYNC bit should remain
high until the flag byte has been detected. Whilst the ESCC device doesn't yet
implement SDLC mode, without this change the active low STATUS_SYNC is constantly
asserted causing the MacOS OpenTransport extension to hang on startup as it thinks
it is constantly receiving LocalTalk responses during its initial negotiation
phase.

Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20210903113223.19551-10-mark.cave-ayland@ilande.co.uk>
Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>