linux-imx

Revert "xen/blkfront: When purging persistent grants, keep them in the buffer"

Fix didn't work for all cases, reverting to add a (hopefully)
better fix.

This reverts commit f151ba989d149bbdfc90e5405724bbea094f9b17.

Signed-off-by: Jens Axboe <axboe@kernel.dk>