strace: fix LARGEFILE typo

Patch by Claus Klein.

package/strace/strace.mk

@@ -28,7 +28,7 @@ $(STRACE_DIR)/.unpacked: $(DL_DIR)/$(STRACE_SOURCE)
 
 $(STRACE_DIR)/.configured: $(STRACE_DIR)/.unpacked
 	(cd $(STRACE_DIR); rm -rf config.cache; \
-		$(if $(BR_LARGEFILE),ac_cv_type_stat64=yes,ac_cv_type_stat64=no) \
+		$(if $(BR2_LARGEFILE),ac_cv_type_stat64=yes,ac_cv_type_stat64=no) \
 		$(TARGET_CONFIGURE_OPTS) \
 		$(TARGET_CONFIGURE_ARGS) \
 		CFLAGS="$(TARGET_CFLAGS) $(BR2_STRACE_CFLAGS)" \