mmc: sh_mmcif: Use platform_get_irq_optional() for optional interrupt

As platform_get_irq() now prints an error when the interrupt does not
exist, a scary warning may be printed for an optional interrupt:

    sh_mmcif ee200000.mmc: IRQ index 1 not found

Fix this by calling platform_get_irq_optional() instead for the second
interrupt, which is optional.

Remove the now superfluous error printing for the first interrupt, which
is mandatory.

Fixes: 7723f4c5 ("driver core: platform: Add an error message to platform_get_irq*()")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Tested-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Tested-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>