btrfs: do not clean up repair bio if submit fails

In the Linux kernel, the following vulnerability has been resolved:

btrfs: do not clean up repair bio if submit fails

The submit helper will always run bio_endio() on the bio if it fails to

submit, so cleaning up the bio just leads to a variety of use-after-free

and NULL pointer dereference bugs because we race with the endio

function that is cleaning up the bio. Instead just return BLK_STS_OK as

the repair function has to continue to process the rest of the pages,

and the endio for the repair bio will do the appropriate cleanup for the

page that it was given.