Tools: hv: kvp: eliminate 'may be used uninitialized' warning

Tools: hv: kvp: eliminate 'may be used uninitialized' warning

When building hv_kvp_daemon GCC-8.3 complains:

hv_kvp_daemon.c: In function ‘kvp_get_ip_info.constprop’:
hv_kvp_daemon.c:812:30: warning: ‘ip_buffer’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  struct hv_kvp_ipaddr_value *ip_buffer;

this seems to be a false positive: we only use ip_buffer when
op == KVP_OP_GET_IP_INFO and it is only unset when op == KVP_OP_ENUMERATE.

Silence the warning by initializing ip_buffer to NULL.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>