pcmcia at91_cf: fix raw gpio number usage

This patches fixes two things:
* Use gpio_valid function to check gpio before usage
  This must be done after 63b4c296 which uses -EINVAL for unused pin's
* Use gpio_to_irq to convert gpio's to irq
  The driver assumed a 1:1 mapping between gpio and irq numbers. This is no
  longer true after d0fbda9a

.

Tested on custom RM9200 board with 8gb CF card.

Signed-off-by: Joachim Eastwood <joachim.eastwood@jotron.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>