staging: gasket: fix DMA direction for extended page tables

Extended page tables should be mapped as DMA_TO_DEVICE, not
bi-directional.

Signed-off-by: Nick Ewalt <nicholasewalt@google.com>
Signed-off-by: Todd Poynor <toddpoynor@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>