fritz-tools: Find zlib.h header file

Add the necessary changes to CMakeLists.txt to search zlib.h. Fixes
build issues with external toolchains that don't have STAGING_DIR in the
default search path.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>

package/utils/fritz-tools/src/CMakeLists.txt

@@ -5,6 +5,9 @@ ADD_DEFINITIONS(-Wall -Werror --std=gnu99 -Wmissing-declarations)
 
 SET(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS "")
 
+FIND_PATH(zlib_include_dir zlib.h)
+INCLUDE_DIRECTORIES(${zlib_include_dir})
+
 ADD_EXECUTABLE(fritz_tffs_read fritz_tffs_read.c)
 ADD_EXECUTABLE(fritz_cal_extract fritz_cal_extract.c)
 TARGET_LINK_LIBRARIES(fritz_cal_extract z)