CMake: Fix cmake_minimum_required() call location warning

[JamiKettunen]

=> noise-suppression-for-voice-1.03-r0: running do_configure...
CMake Warning (dev) at CMakeLists.txt:1 (project):
  cmake_minimum_required() should be called prior to this top-level project()
  call.  Please see the cmake-commands(7) manual for usage documentation of
  both commands.
This warning is for project developers.  Use -Wno-dev to suppress it.