generic/235: Fix false failure on ext2

generic/235: Fix false failure on ext2

The test gives false failure on ext2 filesystem as 64k file already
has indirect block and so space usage does not exactly match
expectation.

The test really needs to verify only whether quota accounting got
reenabled so just test using creating another empty file which is
not prone to these problems.

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>