ANDROID: KVM: Reset the free ffa handle entry

When kvm-arm.ffa-unmap-on-lend is used,
clearing an ff-a handle from the list keeps
an address pointing to the free object. Once
we make use of that object in a sub-sequent
allocation make sure that wwe clear the free
reference.

Bug: 430896873
Change-Id: I4e707d4c692e190292103ad56ce5dba16cabd5af
Signed-off-by: Sebastian Ene <sebastianene@google.com>