In some environments, 100 * nr_active_objs is calculated at first,
and the result of lower 32bits is divided by nr_objs. This occurs
even in a 64-bit architecture. So nr_active_objes > 42949672, %use
will be incorrect.

This fix casts type of nr_active_objs to float to calculate
correctly the %use in 32-bit/64-bit architectures.

Signed-off-by: Takayuki Nagata <tnagata@redhat.com>