Fix make package

Fixes:
CPack: Create package using ZIP
CPack: Install projects
CPack: - Run preinstall target for: direwolf
CPack: - Install project: direwolf []
CMake Error at .../build/conf/cmake_install.cmake:54 (file):
  file INSTALL cannot copy file
  ".../conf/99-direwolf-cmedia.rules"
  to "/etc/udev/rules.d/99-direwolf-cmedia.rules": Permission denied.
Call Stack (most recent call first):
  .../build/cmake_install.cmake:74 (include)

CPack Error: Error when generating package: direwolf
make: *** [Makefile:71: package] Errore 1

Author: dforsi

CMakeLists.txt

@@ -260,6 +260,7 @@ else()
     set(INSTALL_MAN_DIR "share/man/man1")
   endif()
   set(INSTALL_DATA_DIR "share/${PROJECT_NAME}")
+  set(INSTALL_UDEV_DIR "etc/udev/rules.d/")
 endif(WIN32 OR CYGWIN)
 
 # requirements

conf/CMakeLists.txt

@@ -26,7 +26,7 @@ file(WRITE "${CMAKE_BINARY_DIR}/direwolf.conf" "${file_content}")
 
 # install udev rules for CM108
 if(LINUX)
-  install(FILES "${CUSTOM_CONF_DIR}/99-direwolf-cmedia.rules" DESTINATION /etc/udev/rules.d/)
+  install(FILES "${CUSTOM_CONF_DIR}/99-direwolf-cmedia.rules" DESTINATION ${INSTALL_UDEV_DIR})
 endif()
 
 install(FILES "${CMAKE_BINARY_DIR}/direwolf.conf" DESTINATION ${INSTALL_CONF_DIR})