Copy data from the IODMACommand's buffer to the specified buffer.
A byte offset into the IODMACommand's memory, relative to the prepared offset.
The caller supplied buffer to copy the data to.
The length of the data to copy.
The number of bytes copied, zero will be returned if the specified offset is beyond the prepared length of the IODMACommand.
This method copies data from the IODMACommand's memory at the given offset, to the caller's buffer. The IODMACommand must be prepared, and the offset is relative to the prepared offset.