e2fsck: fix unaligned accesses to ext4_fc_tl struct

e2fsck: fix unaligned accesses to ext4_fc_tl struct

Fast commit related struct ext4_fc_tl can be unaligned on disk. So,
while accessing that we should ensure that the pointers are
aligned. This patch fixes unaligned accesses to ext4_fc_tl and also
gets rid of macros fc_for_each_tl and ext4_fc_tag_val that may result
in unaligned accesses to struct ext4_fc_tl.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>