ide-cd: fix "missing data" handling in cdrom_pc_intr()

If drive still wants to transfer the data we need to pad the transfer
instead of just finishing the request.

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>