fuse2fs: fix return value handling

fuse2fs: fix return value handling

For the xattr functions, don't obliterate the return value of the file
system operation with an error code coming from ext2fs_xattrs_close
failing.  Granted, it doesn't ever fail (right now!) so this is mostly
just preening.

Also fix the obsolete op_truncate not to squash error returns.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/174786677978.1383760.8801097477278077188.stgit@frogsfrogsfrogs
Signed-off-by: Theodore Ts'o <tytso@mit.edu>