Fix warn in overwrite-only with slot0 validation
static struct boot_loader_state boot_data;
-#ifdef MCUBOOT_VALIDATE_SLOT0
+#if defined(MCUBOOT_VALIDATE_SLOT0) && !defined(MCUBOOT_OVERWRITE_ONLY)
static int boot_status_fails = 0;
#define BOOT_STATUS_ASSERT(x) \
do { \
