Make __free_tagged actually free memory

Make __free_tagged actually free memory

__free_tagged called by comboot_cleanup_lowmem (core/mem/free.c) doesn't
seem to work correctly. Memory allocated with lmalloc() isn't marked as free
after the allocating module exits:

boot: mem
lowmem_buf: 0x000353e0
boot: mem
lowmem_buf: 0x000553f0
boot: mem
lowmem_buf: 0x00075400
boot: mem
lowmem_buf: 0x00000000
boot:

The expected behaviour

boot: mem
lowmem_buf: 0x000353e0
boot: mem
lowmem_buf: 0x000353e0
boot: mem
lowmem_buf: 0x000353e0

can be achieved with the following patch.