we need to use unique name for firmware dirs, too

mk/vars.mk

@@ -42,7 +42,7 @@ STAGING_HOST_DIR_PFX:=	${BASE_DIR}/host_*
 TARGET_DIR_PFX:=	$(BASE_DIR)/root_*
 
 TARGET_DIR:=		$(BASE_DIR)/root${ADK_SUFFIX}
-FW_DIR:=		$(BASE_DIR)/firmware/${ADK_TARGET_SYSTEM}_${ADK_TARGET_LIBC}
+FW_DIR:=		$(BASE_DIR)/firmware/${ADK_SUFFIX}
 BUILD_DIR:=		${BASE_DIR}/build${ADK_SUFFIX}
 STAGING_TARGET_DIR:=	${BASE_DIR}/target${ADK_SUFFIX}
 STAGING_PKG_DIR:=	${BASE_DIR}/pkg${ADK_SUFFIX}