unify HOST_CFLAGS and HOSTCFLAGS

The top build system sets up HOSTCFLAGS a bit and exports it, but other
places use HOST_CFLAGS instead.  Unify the two as HOSTCFLAGS so that the
values stay in sync.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/board/fads/config.mk b/board/fads/config.mk
index 621b9a2..61060907 100644
--- a/board/fads/config.mk
+++ b/board/fads/config.mk
@@ -30,5 +30,5 @@
 
 TEXT_BASE = 0xFE000000
 PLATFORM_CPPFLAGS += -I$(TOPDIR)/board/fads
-HOST_CFLAGS += -I$(TOPDIR)/board/fads
+HOSTCFLAGS += -I$(TOPDIR)/board/fads
 HOST_ENVIRO_CFLAGS += -I$(TOPDIR)/board/fads