disk: qcow: pass raw file offset in write_cb
disk: qcow: pass raw file offset in write_cb

Modify the write callback function to take the offset into the raw
(backing) file as a parameter rather than seeking to the expected
location of the write. This allows removal of the FileReadWriteVolatile
import in qcow, since this was the last use. This also matches the
read_cb, which already passed the backing file offset explicitly.

BUG=b:219595052
TEST=tools/presubmit

Change-Id: I4ac18d4dbe26e8b196eb8a9c056036565eb39501
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3462641
Reviewed-by: Alexandre Courbot <301cd6a3ea50a894b4b51e385c5eb12b9a4ffc0c@chromium.org>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Commit-Queue: Daniel Verkamp <72bc170b46ec491f7bdd4359a1c0bfed274de40c@chromium.org>

google/crosvm,google/crosvm,google/crosvm,google/crosvm