zlib.c: avoid build conflicts for cradle board

Commit dce3d79710 updated the zlib code to v0.95; this caused
conflicts when building for the "cradle" board, because the (pretty
generic) preprocessor variable "OFF" was used in multiple files.
Make sure to avoid further conflicts by #undef'ing it in zlib.c
before redefining it.

Signed-off-by: Wolfgang Denk <wd@denx.de>
cc: Giuseppe Condorelli <giuseppe.condorelli@st.com>
cc: Angelo Castello <angelo.castello@st.com>
cc: Alessandro Rubini <rubini-list@gnudd.com>

lib_generic/zlib.c

@@ -28,6 +28,8 @@
 
 #include "u-boot/zlib.h"
 #include <common.h>
+#undef	OFF				/* avoid conflicts */
+
 /* To avoid a build time warning */
 #ifdef STDC
 #include <malloc.h>