[LIBS] vfs: ext4: Fix block and inode allocation

Current, ext4fs_control_alloc_block() and ext4fs_control_alloc_inode()
only worked for root node due to minor bugs in these functions.

This patches fixes above described issue in ext4fs_control_alloc_block()
and ext4fs_control_alloc_inode() functions.

Signed-off-by: Anup Patel <anup@brainfault.org>