macintosh/via-macii: Use the stack for reset request storage

The adb_request struct can be stored on the stack because the request
is synchronous and is completed before the function returns.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Stan Johnson <userm57@yahoo.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a40f80dde90991757007b6962c386a208c970586.1593318192.git.fthain@telegraphics.com.au