pcmcia: db1xxx_ss: fix last irq_to_gpio user

remove the usage of removed irq_to_gpio() function.  On pre-DB1200
boards, pass the actual carddetect GPIO number instead of the IRQ,
because we need the gpio to actually test card status (inserted or
not) and can get the irq number with gpio_to_irq() instead.

Tested on DB1300 and DB1500, this patch fixes PCMCIA on the DB1500,
which used irq_to_gpio().

Fixes: 832f5dac

 ("MIPS: Remove all the uses of custom gpio.h")
Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Cc: linux-pcmcia@lists.infradead.org
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Cc: stable@vger.kernel.org	# v4.3+
Patchwork: https://patchwork.linux-mips.org/patch/12747/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>