generic/392: stop checking st_blocks

generic/392: stop checking st_blocks

st_blocks is a rather vaguely defined field.  To quote the Linux stat(2)
man page:

    Use of the st_blocks and st_blksize fields may be less portable.
    (They were introduced in BSD.  The interpretation differs between
    systems, and possibly on a single system when NFS mounts are
    involved.)

or the FreeBSD one:

    st_blocks   Actual number of blocks allocated for the file in
		512-byte units.  As short symbolic links are stored in
		the inode, this number may be zero.

and at least for XFS they include speculative preallocations and
in-flight COW fork allocations, and the numbers can change when the way
how data is stored is reorganized.  Because of that it doesn't make sense
to require st_blocks to not change after a crash even when fsync or
fdatasync was involved.

Remove the st_blocks checks and the now superfluous XFS always_cow
workaround.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>