C++ : Fix error: template with C linkage

If we include this header files in cpp source code,
the compiler say"error: template with C linkage".

Include <device.h> must be moved outside the 'extern "C"' section.

Signed-off-by: Benoit Leforestier <benoit.leforestier@gmail.com>

include/uart.h

@@ -20,15 +20,15 @@
  * @{
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
-
 #include <errno.h>
 #include <stddef.h>
 
 #include <device.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 /** @brief Line control signals. */
 enum uart_line_ctrl {
 	UART_LINE_CTRL_RTS = (1 << 1),