virgl/gbm: fix transfer host plane offset and stride
- Host plane offset queried from the gbm_bo should not be accumulated across plane transfer loop iterations.
- Host plane stride cannot be calculated from host plane0 stride in a generic way, as alignment adjustments cannot be subsampled. Instead of trying of trying to calculate the stride, just query the gbm_bo for it.
Signed-off-by: David Stevens stevensd@chromium.org