libqofono: fix the hardcoded libdir

Fix QA issue when enable multilib:
ERROR: QA Issue: libqofono: Files/directories were installed but not shipped in any package:
  /usr/lib
  /usr/lib/libqofono.so.0.1.0
  /usr/lib/libqofono.so.0
  /usr/lib/libqofono.so.0.1
  /usr/lib/libqofono.so
  /usr/lib/libqofono.prl
  [snip]
Please set FILES such that these items are packaged. Alternatively if they are unneeded, avoid installing them or delete them within do_install. [installed-vs-shipped]

Signed-off-by: Yi Zhao <yi.zhao@windriver.com>