CMakeLists: Use lower-case command names

Our convention uses lower-case command names, so this is just a
consistency change.

CMakeLists.txt

@@ -330,7 +330,7 @@ elseif(SDL2_FOUND)
 endif()
 
 # Ensure libusb is properly configured (based on dolphin libusb include)
-INCLUDE(FindPkgConfig)
+include(FindPkgConfig)
 find_package(LibUSB)
 if (NOT LIBUSB_FOUND)
     add_subdirectory(externals/libusb)