mmc: sdhci: push card_tasklet into threaded irq handler

There's no requirement to have the card tasklet separate now that we
have a threaded interrupt handler, so kill this and move the called
code into the threaded part of the handler.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Tested-by: Markus Pargmann <mpa@pengutronix.de>
Tested-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>