btrfs: fix inode list leak during backref walking at resolve_indirect_refs()

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

btrfs: fix inode list leak during backref walking at resolve_indirect_refs()

During backref walking, at resolve_indirect_refs(), if we get an error

we jump to the 'out' label and call ulist_free() on the 'parents' ulist,

which frees all the elements in the ulist - however that does not free

any inode lists that may be attached to elements, through the 'aux' field

of a ulist node, so we end up leaking lists if we have any attached to

the unodes.

Fix this by calling free_leaf_list() instead of ulist_free() when we exit

from resolve_indirect_refs(). The static function free_leaf_list() is

moved up for this to be possible and it's slightly simplified by removing

unnecessary code.