Fix invalidate if memory requested was not bucket aligned

When memory is mapped in qemu_map_cache with lock != 0 a reverse mapping
is created pointing to the virtual address of location requested.
The cached mapped entry is saved in last_address_vaddr with the memory
location of the base virtual address (without bucket offset).
However when this entry is invalidated the virtual address saved in the
reverse mapping is used. This cause that the mapping is freed but the
last_address_vaddr is not reset.

Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
