ext4: Change list_for_each* to list_for_each_entry*

In the fast_commit.c, list_for_each* + list_entry can be changed to
list_for_each_entry*. It reduces number of variables and lines.

Signed-off-by: Daejun Park <daejun7.park@samsung.com>
Link: https://lore.kernel.org/r/20210111013726epcms2p4579ae56040d7043db785bf0d0a785dc7@epcms2p4
Signed-off-by: Theodore Ts'o <tytso@mit.edu>