iommu/qcom: Use domain rather than dev as tlb cookie

The device may be torn down, but the domain should still be valid.  Lets
use that as the tlb flush ops cookie.

Fixes a problem reported in [1]

[1] https://lkml.org/lkml/2020/7/20/104

Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Fixes: 09b5dfff

 ("iommu/qcom: Use accessor functions for iommu private data")
Link: https://lore.kernel.org/r/20200720155217.274994-1-robdclark@gmail.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>