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/pwm/pwm.c

@@ -233,7 +233,7 @@ mraa_pwm_init(int pin)
         syslog(LOG_ERR, "pwm_init: pin %i beyond platform definition", pin);
         return NULL;
     }
-    if (board->pins[pin].capabilites.pwm != 1) {
+    if (board->pins[pin].capabilities.pwm != 1) {
         syslog(LOG_ERR, "pwm_init: pin %i not capable of pwm", pin);
         return NULL;
     }