Fixed compile warnings

include/sta/bus/spi/spi.hpp

@@ -31,6 +31,7 @@ namespace sta
          */
         SPI(const SPISettings & settings, Mutex * mutex = nullptr);
 
+        using Interface::transfer;
         /**
 		 * @brief Send and receive data simultaneously.
 		 *

src/bus/spi/device.cpp

@@ -21,7 +21,7 @@ namespace sta
 		STA_ASSERT(txBuffer != nullptr);
 		STA_ASSERT(rxBuffer != nullptr);
 
-		intf_->transfer(txBuffer, rxBuffer, size, timeout);
+		return intf_->transfer(txBuffer, rxBuffer, size, timeout);
 	}
 
     const SPISettings & SPIDevice::settings() const

src/devices/stm32/bus/spi.cpp

@@ -154,6 +154,8 @@ namespace sta
                 return HAL_SPI_Transmit(handle_, reinterpret_cast<uint8_t *>(&dummy), 1, timeout) == HAL_OK;
             }
         }
+
+        return false;
     }
 
     STM32SPIDevice::STM32SPIDevice(STM32SPI * intf, STM32GpioPin * csPin)