boards/avr/avrdx/breadxavr: silence unused variable warning

This patch silences a warning caused by unconditionally declared
variable which is only used with specific configuration.

Also, if the initialization fails, panic instead of returning.
(This should not happen since the code runs in initialization
phase but silently returning is not the correct action.)

Signed-off-by: Kerogit <[email protected]>

Author: Kerogit

boards/avr/avrdx/breadxavr/src/avrdx_init.c

@@ -32,6 +32,7 @@
 #  include <nuttx/input/buttons.h>
 #endif
 
+#include <assert.h>
 #include <avr/io.h>
 
 #include "avrdx_gpio.h"
@@ -77,13 +78,15 @@
 #ifdef CONFIG_BOARD_EARLY_INITIALIZE
 void board_early_initialize(void)
 {
+#  ifdef CONFIG_BREADXAVR_BUTTONS_DRIVER
   int ret = OK;
+#  endif
 
 #  ifdef CONFIG_BREADXAVR_BUTTONS_DRIVER
   ret = btn_lower_initialize("/dev/buttons");
   if (ret != OK)
     {
-      return;
+      PANIC();
     }
 #  endif
 }