[SUASH ME] cpu/stm32f0: reacted to cppcheck warnings

cpu/stm32f0/periph/spi.c

@@ -31,10 +31,10 @@
 
 int spi_init_master(spi_t dev, spi_conf_t conf, spi_speed_t speed)
 {
-    SPI_TypeDef *spi = 0;
-    GPIO_TypeDef *port = 0;
+    SPI_TypeDef *spi;
+    GPIO_TypeDef *port;
     int pin[3];        /* 3 pins: sck, miso, mosi */
-    int af;
+    int af = 0;
 
     /* power on the SPI device */
     spi_poweron(dev);
@@ -62,6 +62,8 @@ int spi_init_master(spi_t dev, spi_conf_t conf, spi_speed_t speed)
             SPI_0_PORT_CLKEN();
             break;
 #endif
+        default:
+            return -1;
     }
 
     /* configure pins for their correct alternate function */
@@ -133,6 +135,8 @@ int spi_transfer_byte(spi_t dev, char out, char *in)
             spi = SPI_1_DEV;
             break;
 #endif
+        default:
+            return 0;
     }
 
     /* wait for an eventually previous byte to be readily transferred */
@@ -154,20 +158,21 @@ int spi_transfer_byte(spi_t dev, char out, char *in)
 int spi_transfer_bytes(spi_t dev, char *out, char *in, unsigned int length)
 {
     char res;
+    int count = 0;
 
     for (int i = 0; i < length; i++) {
         if (out) {
-            spi_transfer_byte(dev, out[i], &res);
+            count += spi_transfer_byte(dev, out[i], &res);
         }
         else {
-            spi_transfer_byte(dev, 0, &res);
+            count += spi_transfer_byte(dev, 0, &res);
         }
         if (in) {
             in[i] = res;
         }
     }
 
-    return length;
+    return count;
 }
 
 int spi_transfer_reg(spi_t dev, uint8_t reg, char out, char *in)