arch/arm/src/stm32/stm32_adc.c: Eliminate a new warning found in build testing

TODO

@@ -1,4 +1,4 @@
-NuttX TODO List (Last updated November 29, 2018)
+NuttX TODO List (Last updated December 3, 2018)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 This file summarizes known NuttX bugs, limitations, inconsistencies with
@@ -1493,6 +1493,15 @@ o Network (net/, drivers/net)
                immediately (unless the SO_LINGER option is selected).  As a
                result, the socket does not send the FIN and this looks like
                an unexpected, abnormal loss of connection to the remote peer.
+
+               Actually, it is worse than this:  The is NO logic to send
+               FIN in when the file is close.  This is pretty easy to do,
+               however:
+
+                 - Wait for a TCP poll, then
+                 - Call tcp_append with TCP_CLOSE in the flags.  There is
+                   already logic in tcp_appsend to send the FIN in this case,
+                   it is just not being use.
   Status:      Open
   Priority:    Medium-Low.
 

arch/arm/src/stm32/stm32_adc.c

@@ -2527,8 +2527,6 @@ static void adc_voltreg_cfg(FAR struct stm32_dev_s *priv)
 
 static void adc_sampletime_cfg(FAR struct adc_dev_s *dev)
 {
-  FAR struct stm32_dev_s *priv = (FAR struct stm32_dev_s *)dev->ad_priv;
-
   /* Initialize the same sample time for each ADC.
    * During sample cycles channel selection bits must remain unchanged.
    */
@@ -2536,6 +2534,8 @@ static void adc_sampletime_cfg(FAR struct adc_dev_s *dev)
 #ifdef CONFIG_STM32_ADC_CHANGE_SAMPLETIME
   adc_sampletime_write((FAR struct stm32_adc_dev_s *)dev);
 #else
+  FAR struct stm32_dev_s *priv = (FAR struct stm32_dev_s *)dev->ad_priv;
+
   adc_putreg(priv, STM32_ADC_SMPR1_OFFSET, ADC_SMPR1_DEFAULT);
   adc_putreg(priv, STM32_ADC_SMPR2_OFFSET, ADC_SMPR2_DEFAULT);
 #  ifdef STM32_ADC_SMPR3_OFFSET