ocfs2: Make global quota files blocksize aligned

Change i_size of global quota files so that it always remains aligned to block
size. This is mainly because the end of quota block may contain checksum (if
checksumming is enabled) and it's a bit awkward for it to be "outside" of quota
file (and it makes life harder for ocfs2-tools).

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Joel Becker <joel.becker@oracle.com>