fix #2874: SATA: avoid unsolicited write to sector 0 during reset
If there is a pending DMA operation during ide_bus_reset(), the fact
that the IDEstate is already reset before the operation is canceled
can be problematic. In particular, ide_dma_cb() might be called and
then use the reset IDEstate which contains the signature after the
reset. When used to construct the IO operation this leads to
ide_get_sector() returning 0 and nsector being 1. This is particularly
bad, because a write command will thus destroy the first sector which
often contains a partition table or similar.