Properly set CMAKE_INSTALL_PREFIX to /usr by default

CMakeLists.txt

@@ -1,6 +1,11 @@
 cmake_minimum_required(VERSION 3.13)
 project(sdrpp)
 
+# Default to /usr for CMAKE_INSTALL_PREFIX
+if (CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
+    set(CMAKE_INSTALL_PREFIX "/usr" CACHE PATH "Default install prefix" FORCE)
+endif()
+
 option(OPT_BUILD_RTL_TCP_SOURCE "Build RTL-TCP Source Module (no dependencies required)" ON)
 option(OPT_BUILD_SPYSERVER_SOURCE "Build SpyServer Source Module (no dependencies required)" ON)
 option(OPT_BUILD_SOAPY_SOURCE "Build SoapySDR Source Module (Depedencies: soapysdr)" ON)
@@ -86,11 +91,6 @@ endif ()
 
 # cmake .. "-DCMAKE_TOOLCHAIN_FILE=C:/Users/Alex/vcpkg/scripts/buildsystems/vcpkg.cmake" -G "Visual Studio 15 2017 Win64"
 
-# Default to /usr for CMAKE_INSTALL_PREFIX
-if (CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
-    set(CMAKE_INSTALL_PREFIX "/usr" CACHE PATH "Default install prefix" FORCE)
-endif()
-
 # Install directives
 install(TARGETS sdrpp DESTINATION bin)
 install(DIRECTORY ${CMAKE_SOURCE_DIR}/root/res/bandplans DESTINATION share/sdrpp)