[XFS] remove permission check from xfs_change_file_space

Both callers of xfs_change_file_space alreaedy do the file->f_mode &
FMODE_WRITE check to ensure we have a file descriptor that has been opened
for write mode, so there is no need to re-check that with xfs_iaccess.
Especially as the later might wrongly deny it for corner cases like file
descriptor passing through unix domain sockets.

SGI-PV: 971186
SGI-Modid: xfs-linux-melb:xfs-kern:30365a

Signed-off-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Lachlan McIlroy <lachlan@sgi.com>