open2300: fix build on macos

This patch sets UNAME=Linux due to OpenWrt is always Linux but
`uname -s` return Darwin on MacOS and fails target build.

Signed-off-by: Sergey V. Lobanov <sergey@lobanov.in>

utils/open2300/Makefile

@@ -12,7 +12,7 @@ include $(TOPDIR)/rules.mk
 PKG_NAME:=open2300
 PKG_SOURCE_DATE:=2014-03-04
 PKG_SOURCE_VERSION:=1af8ae609da66f8e1b745533c19095c9758bfb0b
-PKG_RELEASE:=2
+PKG_RELEASE:=3
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL:=https://github.com/wezm/open2300
@@ -35,6 +35,9 @@ define Package/open2300/description
   This is an utility suite used to communicate with and collect data from a WS23XX wheather station.
 endef
 
+MAKE_FLAGS += \
+	UNAME=Linux
+
 define Package/open2300/install
 	$(INSTALL_DIR) $(1)/usr/bin
 	$(INSTALL_BIN) $(PKG_BUILD_DIR)/bin2300		$(1)/usr/bin/