macintosh/adb-iop: Send correct poll command

The behaviour of the IOP firmware is not well documented but we do know
that IOP message reply data can be used to issue new ADB commands.
Use the message reply to better control autopoll behaviour by sending
a Talk Register 0 command after every ADB response, not unlike the
algorithm in the via-macii driver. This poll command is addressed to
that device which last received a Talk command (explicit or otherwise).

Cc: Joshua Thompson <funaho@jurai.org>
Fixes: 32226e81 ("macintosh/adb-iop: Implement idle -> sending state transition")
Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Link: https://lore.kernel.org/r/58bba4310da4c29b068345a4b36af8a531397ff7.1605847196.git.fthain@telegraphics.com.au


Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>