ide-atapi: start DMA after issuing a packet command

ide-atapi: start DMA after issuing a packet command

upstream commit: 2eba08270990b99fb5429b76ee97184ddd272f7f

Apparently¹, some ATAPI devices want to see the packet command first
before enabling DMA otherwise they simply hang indefinitely. Reorder the
two steps and start DMA only after having issued the command first.

[1] http://marc.info/?l=linux-kernel&m=123835520317235&w=2

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
Reported-by: Michael Roth <mroth@nessie.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>