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/xilinx/ppc440-generic/Makefile b/board/xilinx/ppc440-generic/Makefile
index bf0a6ba..11a8f69 100644
--- a/board/xilinx/ppc440-generic/Makefile
+++ b/board/xilinx/ppc440-generic/Makefile
@@ -31,7 +31,7 @@
 
 INCS		:=
 CFLAGS		+= $(INCS)
-HOST_CFLAGS	+= $(INCS)
+HOSTCFLAGS	+= $(INCS)
 
 LIB	= $(obj)lib$(BOARD).a