ext4: simplify journal handling in setup_new_group_blocks()

This patch simplifies journal handling in setup_new_group_blocks().

In previous code, block bitmap is modified everywhere in
setup_new_group_blocks(), ext4_get_write_access() in
extend_or_restart_transaction() is used to guarantee that the block
bitmap stays in the new handle, this makes things complicated.

The previous commit changed things so that the modifications on the
block bitmap are batched and done by ext4_set_bits() at the end of the
for loop.  This allows us to simplify things.

Signed-off-by: Yongqiang Yang <xiaoqiangnk@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>