mmc: davinci: Make SDIO irq truly optional

The following error is printed on Logic PD's DA850 EVM:
  davinci_mmc 1c40000.mmc: error -ENXIO: IRQ index 1 not found

Depending on the board, the SDIO interrupt may not be present, so use
the correct function to reflect that and prevent logging an error.

Signed-off-by: Julien Delbergue <j.delbergue.foss@gmail.com>
Acked-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://lore.kernel.org/r/8b57db8d-1d3a-883e-eb8f-ddf15f19d823@gmail.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>