qt5multimedia: fix installation when quick is disabled

Fixes:

  http://autobuild.buildroot.net/results/b97/b975c4bb8aebad2d0b8eaefc98c42c0460ace5be/
  http://autobuild.buildroot.net/results/b1c/b1ca9c845f1cf3a396cbd7ad81bfc4411974c709/

Signed-off-by: Fatih Aşıcı <fatih.asici@gmail.com>