CMake: Set install MacOSX Framework location to `CMAKE_INSTALL_PREFIX`

Users should be able to install the MacOSX Framework by pointing
CMAKE_INSTALL_PREFIX to the corresponding directory. For example to
install into `/Library/Frameworks` configure with

cmake -DCMAKE_INSTALL_PREFIX=/Library/Frameworks <build dir>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 14c96f1..78b6604 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -108,7 +108,7 @@
     RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
     LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
     ARCHIVE DESTINATION ${CMAKE_INSTALL_LIBDIR}
-    FRAMEWORK DESTINATION ${CMAKE_INSTALL_LIBDIR}
+    FRAMEWORK DESTINATION ${CMAKE_INSTALL_PREFIX}
     PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/ogg
 )
 install(FILES ogg.pc DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig)