Fix some warnings

git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@4318 42af7a65-404d-4744-a932-0658087f49c3

configs/stm3210e-eval/src/up_adc.c

@@ -40,6 +40,7 @@
 
 #include <nuttx/config.h>
 
+#include <errno.h>
 #include <debug.h>
 
 #include <nuttx/analog/adc.h>
@@ -137,7 +138,7 @@ int adc_devinit(void)
       if (adc == NULL)
         {
           adbg("ERROR: Failed to get ADC interface\n");
-          return;
+          return -ENODEV;
         }
 
       /* Register the ADC driver at "/dev/adc0" */
@@ -161,4 +162,4 @@ int adc_devinit(void)
 }
 
 #endif /* CONFIG_STM32_ADC1 || CONFIG_STM32_ADC2 || CONFIG_STM32_ADC3 */
-#endif /* CONFIG_ADC */
\ No newline at end of file
+#endif /* CONFIG_ADC */