xfs_io: don't fail FS_IOC_FSGETXATTR on filesystems that lack support

xfs_io: don't fail FS_IOC_FSGETXATTR on filesystems that lack support

Not all filesystems implement the FS_IOC_FSGETXATTR ioctl, and in those
cases -ENOTTY will be returned. There is no need to return with an error
when this happens, so just silently return.

Without this fstest generic/169 fails on NFS that doesn't implement the
fileattr_get inode operation.

Fixes: e6b48f451a5d ("xfs_io: allow foreign FSes to show FS_IOC_FSGETXATTR details")
Signed-off-by: Anthony Iliopoulos <ailiop@suse.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>