Fix to use correct build flag MBED_CONF_NANOSTACK_CONFIGURATION

The bare-metal configuration should be using MBED_CONF_NANOSTACK_CONFIGURATION
instead of MBED_CONF_NANOSTACK_CONFIG.

Fixing the typo for flagging.

Author: Yogesh Pande

features/nanostack/nanostack-hal-mbed-cmsis-rtos/arm_hal_fhss_timer.cpp

@@ -15,7 +15,7 @@
  * limitations under the License.
  */
 
-#ifdef MBED_CONF_NANOSTACK_CONFIG
+#ifdef MBED_CONF_NANOSTACK_CONFIGURATION
 
 #include "ns_types.h"
 #include "fhss_api.h"