Initialize the allocation of variables related to the ext2 allocator.

Initialize the allocation of variables related to the ext2 allocator.

The e2fs_gd struct was not being initialized and garbage was
being used for hinting the ext2 allocator variant.
Use malloc to clear the values and also initialize e2fs_contigdirs
during allocation to keep consistency.

While here clean up small style issues.

Reported by:	Clang static analyser
MFC after:	1 week