hv: utils: handle and propagate errors in kvp_register

hv: utils: handle and propagate errors in kvp_register

Make kvp_register() return an error code instead of silently ignoring
failures, and propagate the error from kvp_handle_handshake() instead of
returning success.

This propagates both kzalloc_obj() and hvutil_transport_send() failures
to kvp_handle_handshake() and thus to kvp_on_msg().

Fixes: 245ba56a52a3 ("Staging: hv: Implement key/value pair (KVP)")
Cc: stable@vger.kernel.org
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Long Li <longli@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>