accel/amdxdna: put the chained BO when its mapping fails

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

accel/amdxdna: put the chained BO when its mapping fails

amdxdna_cmd_set_error() looks up the first BO of a command chain, which
takes a reference, and drops it at the end of the function. The mapping of
that BO is established in between, and the failure path returns without the
put, so the reference is leaked.

Ordinary use does not reach it. The chain has been submitted before any of
this runs, so aie2_cmdlist_fill_slot() has already called
amdxdna_cmd_get_op() on that BO and amdxdna_gem_vmap() has cached its
address. What makes it reachable is that the BO is resolved again by
handle here, and the handle is userspace's to recycle: closing it after
submission and importing a dma-buf whose exporter implements no vmap onto
the same id leaves amdxdna_gem_get_obj() returning an object this cannot
map, since prime_import() types every import AMDXDNA_BO_SHARE.