ide: Clear DRQ after handling all expected accesses (CVE-2015-5154)

ide: Clear DRQ after handling all expected accesses (CVE-2015-5154)

This is additional hardening against an end_transfer_func that fails to
clear the DRQ status bit. The bit must be unset as soon as the PIO
transfer has completed, so it's better to do this in a central place
instead of duplicating the code in all commands (and forgetting it in
some).

upstream-commit-id: cb72cba83021fa42719e73a5249c12096a4d1cfc

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>