STM32 I2C: Bring in PX4 fix for I2C in very high noise environments or with rogue perpipherals. Taken from the PX4 commit by Tridge

arch/arm/src/stm32/Kconfig

@@ -698,7 +698,6 @@ config STM32_STM32F207
 	default n
 	select STM32_HAVE_OTGFS
 	select STM32_HAVE_FSMC
-	select STM32_HAVE_CCM
 	select STM32_HAVE_USART3
 	select STM32_HAVE_USART4
 	select STM32_HAVE_USART5

arch/arm/src/stm32/stm32_i2c.c

@@ -1617,7 +1617,14 @@ static int stm32_i2c_process(FAR struct i2c_dev_s *dev, FAR struct i2c_msg_s *ms
 
   stm32_i2c_clrstart(priv);
 
-  /* Old transfers are done */
+  /* Old transfers are done
+   *
+   * Reset ptr and dcnt to ensure an unexpected data interrupt doesn't
+   * overwrite stale data.
+   */
+
+  priv->dcnt = 0;
+  priv->ptr  = NULL;
 
   priv->msgv = msgs;
   priv->msgc = count;
@@ -1754,6 +1761,11 @@ static int stm32_i2c_process(FAR struct i2c_dev_s *dev, FAR struct i2c_msg_s *ms
   stm32_i2c_enablefsmc(ahbenr);
   stm32_i2c_sem_post(dev);
 
+  /* Ensure that any ISR happening after we finish can't overwrite any user data */
+
+  priv->dcnt = 0;
+  priv->ptr  = NULL;
+
   return -errval;
 }