kvm: x86: i8259: return initialized data on invalid-size read

If data is read from PIC with invalid access size, the return data stays
uninitialized even though success is returned.

Fix this by always initializing the data.

Signed-off-by: Petr Matousek <pmatouse@redhat.com>
Reported-by: Nadav Amit <nadav.amit@gmail.com>
Message-Id: <20150311111609.GG8544@dhcp-25-225.brq.redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>