macintosh/via-macii: Synchronous bus reset

Make the reset operation synchronous, like the other ADB drivers.
The reset request is static data but callers may not know that.
This way the struct is not in use when the reset method returns.

Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>