resize2fs: fix -M size calculations to avoid cutting off the inode table

resize2fs: fix -M size calculations to avoid cutting off the inode table

If the file system's inode table blocks in the last block group are
located in the middle or the end of the block group, it's possible for
resize2fs -M to use a size which will require relocating the inode
table blocks in the last block group.  This can lead to all sorts of
problems, so solve it by simply guaranteeing that we will never do
that.

Reported-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>