mmc: omap_hsmmc: remove unused slot_id parameter

omap_hsmmc only supports one slot. So slot id is always zero, and
slot id was never used in the callbacks anyway

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