sh-pfc: Don't overallocate memory for the GPIO chip pins array

The GPIO driver uses an array of sh_pfc_gpio_pin structures to store
per-GPIO pin data. The array size is miscomputed at allocation time by
using the number of the last pin instead of the number of pins. When the
pin space contains holes this leads to memory overallocation. Fix it.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Tested-by: Yusuke Goda <yusuke.goda.sx@renesas.com>