mraa: Correct spelling of capabilities

Type was correctly spelt, but the member in the platform strut was not.
My mistake from 2014.

Signed-off-by: Thomas Ingleby <thomas.ingleby@intel.com>

src/gpio/gpio.c

@@ -151,7 +151,7 @@ mraa_gpio_init(int pin)
         syslog(LOG_ERR, "gpio: init: pin %i beyond platform pin count (%i)", pin, board->phy_pin_count);
         return NULL;
     }
-    if (board->pins[pin].capabilites.gpio != 1) {
+    if (board->pins[pin].capabilities.gpio != 1) {
         syslog(LOG_ERR, "gpio: init: pin %i not capable of gpio", pin);
         return NULL;
     }