libext2fs: fix regression so we are correctly translating Posix ACL's

libext2fs: fix regression so we are correctly translating Posix ACL's

The commit 50d0998cfee ("libext2fs: add ea_inode support to set
xattr") broke the fix that was addressed in commit 0ee1eaf70c25
("libext2fs: translate internal ext4 acl to Posix ACL in
ext2fs_xattr_[sg]et()").  This was because although we calculated what
the correct on-disk ACL representation would be, we didn't actually
*store* it, but instead stored the passed-in Posix ACL memory
representation instead.

Addresses-Launchpad-Bug: #1807288
Signed-off-by: Theodore Ts'o <tytso@mit.edu>