Bluetooth: Use correct struct for user_confirm_neg_reply

This patch fixes user_confirm_neg_reply to use the appropriate struct
for accessing the call parameters.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>