[XFS] pass inode to xfs_ioc_space(), simplify some code. There is trivial

"inode => vnode => inode" conversion, but only flags and mode of final
inode are looked at. Pass original inode instead.

SGI-PV: 904196
SGI-Modid: xfs-linux-melb:xfs-kern:26395a

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Nathan Scott <nathans@sgi.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>