mmc: fix rmmod race for hosts using card-detection polling

mmc: fix rmmod race for hosts using card-detection polling

commit d9bcbf343ec63e1104b5276195888ee06b4d086f upstream.

MMC hosts that poll for card detection by defining the MMC_CAP_NEEDS_POLL
flag have a race on rmmod, where the delayed work is cancelled without
waiting for completed polling. To prevent this a _sync version of the work
cancellation has to be used.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>