Fix leak of pwm enable file descriptor (#197)

Make sure that the file descriptor for pwm enable
is closed along with the other pwm file descriptors

Signed-off-by: Drew Fustini <drew@pdp7.com>

source/c_pwm.c

@@ -553,6 +553,9 @@ BBIO_err pwm_setup(const char *key, __attribute__ ((unused)) float duty, __attri
         close(period_fd);
         close(duty_fd);
         close(polarity_fd);
+#ifdef BBBVERSION41
+        close(enable_fd);
+#endif
         syslog(LOG_ERR, "Adafruit_BBIO: pwm_setup: %s couldn't malloc pwm_exp: %i-%s",
                key, errno, strerror(errno));
         return BBIO_MEM; // out of memory