floppy: cleanups: use memcpy() to copy reply_buffer

Use memcpy() in raw_cmd_done() to copy reply_buffer instead
of a for loop.

Signed-off-by: Denis Efremov <efremov@linux.com>
Link: https://lore.kernel.org/r/20210416083449.72700-5-efremov@linux.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>