mmc: slot-gpio: Remove unused mmc_gpio_set_cd_isr

mmc_gpio_set_cd_isr() last use was removed in 2018 by
commit 7838a8dd ("mmc: omap_hsmmc: Kill off cover detection")

Remove it.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://lore.kernel.org/r/20250129214335.125292-1-linux@treblig.org


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