mmc: core: Clean up after mmc_pre_req if card was removed

Make sure mmc_start_req cancels the prepared job, if the request
was prevented to be started due to the card has been removed.

This bug was introduced in commit:
mmc: allow upper layers to know immediately if card has been removed

Signed-off-by: Ulf Hansson <ulf.hansson@stericsson.com>
Reviewed-by: Per Forlin <per.forlin@stericsson.com>
Tested-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>