ext4: free allocations by parse_path()

parse_path() malloc()s the entries in the array it's passed. Those
allocations must be free()d by the caller, ext4fs_get_parent_inode_num().
Add code to do this.

For this to work, all the array entries must be dynamically allocated,
rather than a mix of dynamic and static allocations. Fix parse_path() not
to over-write arr[0] with a pointer to statically allocated data.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Lukasz Majewski <l.majewski@samsung.com>
Tested-by: Lukasz Majewski <l.majewski@samsung.com>