All external users of sdio_run_irqs() have converted into using the
preferred sdio_signal_irq() interface, thus not calling the function
directly any more. Avoid further new users of it, by turning it into
static.

Suggested-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>