Fixing trivial warnings for libminui

After fixing three trivial warnings, libminui builds cleanly with clang.

Change-Id: Id7c6228295427a5ed3c774c5f90e88a28336c1f7
Author: Edwin Vane <edwin.vane@intel.com>
Reviewed-by: Kevin P Schoedel <kevin.p.schoedel@intel.com>