xfstests: fix xfs/205 for new log size defaults

xfstests: fix xfs/205 for new log size defaults

test xfs/205 expects a certain log size, but defaults have
changed, the logs are bigger, and this test now fails w/ early
ENOSPC:

     QA output created by 205
    +   !!! disk full (expected)
    +   !!! disk full (expected)
    +   !!! disk full (expected)
     *** one file
    +   !!! disk full (expected)
     *** one file, a few bytes at a time
     ...

Fix this by specifying the log size at mkfs time, so freespace is
as the test expects it to be.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>