mmc: rtsx: init cookie at probe/card_event

host->cookie is used for handle async request,
we should init it to negative value when new card inserted,
make cookie value invalid.

Signed-off-by: Micky Ching <micky_ching@realsil.com.cn>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>