jbd2: move superblock checksum calculation to jbd2_write_superblock()

commit fe52d17cdd343ac43c85cf72940a58865b9d3bfb upstream.

Some of the functions which modify the jbd2 superblock were not
updating the checksum before calling jbd2_write_superblock().  Move
the call to jbd2_superblock_csum_set() to jbd2_write_superblock(), so
that the checksum is calculated consistently.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>