drivers/gpio/ml_ioh_gpio.c needs slab.h

alpha allmodconfig:

  drivers/gpio/ml_ioh_gpio.c: In function 'ioh_gpio_probe':
  drivers/gpio/ml_ioh_gpio.c:205: error: implicit declaration of function 'kzalloc'
  drivers/gpio/ml_ioh_gpio.c:205: warning: assignment makes pointer from integer without a cast

also fix this:

  drivers/gpio/ml_ioh_gpio.c:145: warning: 'ioh_gpio_save_reg_conf' defined but not used
  drivers/gpio/ml_ioh_gpio.c:154: warning: 'ioh_gpio_restore_reg_conf' defined but not used

Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>