block: unalign call_single_data in struct request

commit 4ccafe032005e9b96acbef2e389a4de5b1254add upstream.

A previous change blindly added massive alignment to the
call_single_data structure in struct request. This ballooned it in size
from 296 to 320 bytes on my setup, for no valid reason at all.

Use the unaligned struct __call_single_data variant instead.

Fixes: 966a9671 ("smp: Avoid using two cache lines for struct call_single_data")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>