mmc: omap_hsmmc: remove unnecessary omap_hsmmc_slot_data indirection

omap_hsmmc supports only one slot per controller, see OMAP_MMC_MAX_SLOTS.
This unnecessary indirection leads to confusion in the omap_hsmmc driver.
For example the card_detect callback is not installed by platform code
but from the driver probe function. So it should be a field of
omap_hsmmc_host. But since it is declared under the platform slot while
the drivers struct omap_hsmmc_host has no slot abstraction, this looks
like a bug, especially when not familiar that this driver only supports
1 slot anyway.
Either we should add a slot abstraction to omap_hsmmc_host or remove
it from the platform data struct. Removed since slot multiplexing is
an un-implemented feature

Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Andreas Fenkart <afenkart@gmail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>