arm/lpc176x: Address unused parameter warnings

Add "(void) param;" annotation to address unused parameter warnings.
Found with GCC's warning -Wunused-parameter.

bsps/arm/lpc176x/btimer/btimer.c

@@ -44,4 +44,5 @@ benchmark_timer_t benchmark_timer_read( void )
 
 void benchmark_timer_disable_subtracting_average_overhead( bool find_avg_ovhead )
 {
+  (void) find_avg_ovhead;
 }

bsps/arm/lpc176x/can/can.c

@@ -407,6 +407,8 @@ static inline void search_and_call_int( const lpc176x_can_number number )
  */
 static void can_isr( void *arg )
 {
+  (void) arg;
+
   lpc176x_can_number i;
 
   for ( i = CAN_0; i < CAN_DEVICES_NUMBER; ++i ) {

bsps/arm/lpc176x/gpio/lpc-gpio.c

@@ -181,6 +181,8 @@ static void check_for_interrupt(
  */
 static inline void lpc176x_gpio_isr( void *arg )
 {
+  (void) arg;
+
   unsigned int i;
 
   for ( i = 0; i < function_vector_size; ++i ) {

bsps/arm/lpc176x/pwm/pwmout.c

@@ -125,6 +125,8 @@ static void set_period(
   const lpc176x_microseconds period
 )
 {
+  (void) pwm;
+
   pwm_device->TCR = PWM_TCR_RESET;
   pwm_device->MR0 = period * PWM_PRESCALER_USECOND;
   pwm_device->LER |= PWM_LER_LATCH_MATCH_0;

bsps/arm/lpc176x/start/bspidle.c

@@ -38,6 +38,8 @@
 
 void*bsp_idle_thread( const uintptr_t ignored )
 {
+  (void) ignored;
+
   while ( true ) {
   }
 }

bsps/arm/lpc176x/start/dma-copy.c

@@ -42,6 +42,8 @@ static bool     lpc176x_dma_status_table[ GPDMA_CH_NUMBER ];
 
 static void lpc176x_dma_copy_handler( void *arg )
 {
+  (void) arg;
+
   /* Get interrupt status */
   uint32_t tc = GPDMA_INT_TCSTAT;
   uint32_t err = GPDMA_INT_ERR_STAT;