More cleanup to convert open-coded calculations of the first block
number of a free extent to use ext4_grp_offs_to_block() instead.
Signed-off-by: NAkinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger@sun.com>