auto_init: Print correct SPI bus in DEBUG output

sys/auto_init/netif/auto_init_at86rf2xx.c

@@ -44,8 +44,9 @@ static char _nomac_stacks[AT86RF2XX_MAC_STACKSIZE][AT86RF2XX_NUM];
 void auto_init_at86rf2xx(void)
 {
     for (unsigned i = 0; i < AT86RF2XX_NUM; i++) {
-        DEBUG("Initializing AT86RF2xx radio at SPI_%i\n", i);
         const at86rf2xx_params_t *p = &at86rf2xx_params[i];
+
+        DEBUG("Initializing AT86RF2xx radio at SPI_%i\n", p->spi);
         int res = at86rf2xx_init(&at86rf2xx_devs[i],
                                  p->spi,
                                  p->spi_speed,

sys/auto_init/netif/auto_init_kw2xrf.c

@@ -46,9 +46,9 @@ static char _nomac_stacks[KW2XRF_MAC_STACKSIZE][KW2XRF_NUM];
 void auto_init_kw2xrf(void)
 {
     for (int i = 0; i < KW2XRF_NUM; i++) {
-        DEBUG("Initializing KW2xrf radio at SPI_%i\n", i);
         const kw2xrf_params_t *p = &kw2xrf_params[i];
 
+        DEBUG("Initializing KW2xrf radio at SPI_%i\n", p->spi);
         int res = kw2xrf_init(&kw2xrf_devs[i],
                 p->spi,
                 p->spi_speed,