cc2538_rf: use prefix for global function name

cpu/cc2538/include/cc2538_rf.h

@@ -220,7 +220,7 @@ typedef struct {
  * @brief   IRQ handler for RF events
  *
  */
-void _irq_handler(void);
+void cc2538_irq_handler(void);
 
 /**
  * @brief   Trigger a clear channel assessment

cpu/cc2538/radio/cc2538_rf_internal.c

@@ -64,7 +64,7 @@ void isr_rfcoreerr(void)
 
 void isr_rfcorerxtx(void)
 {
-   _irq_handler();
+   cc2538_irq_handler();
 
     cortexm_isr_end();
 }

cpu/cc2538/radio/cc2538_rf_netdev.c

@@ -34,7 +34,7 @@
 /* Reference pointer for the IRQ handler */
 static netdev_t *_dev;
 
-void _irq_handler(void)
+void cc2538_irq_handler(void)
 {
     RFCORE_SFR_RFIRQF0 = 0;
     RFCORE_SFR_RFIRQF1 = 0;

cpu/cc2538/radio/cc2538_rf_radio_ops.c

@@ -307,7 +307,7 @@ static int _request_set_trx_state(ieee802154_dev_t *dev, ieee802154_trx_state_t
     return 0;
 }
 
-void _irq_handler(void)
+void cc2538_irq_handler(void)
 {
     uint_fast8_t flags_f0 = RFCORE_SFR_RFIRQF0;
     uint_fast8_t flags_f1 = RFCORE_SFR_RFIRQF1;