sparc64: Fix for perf event counts sometimes reported as negative numbers

sparc64: Fix for perf event counts sometimes reported as negative numbers

Use an unsigned number to prevent sign extension in the calculation
to work out the difference between the previous and the current
count obtained from the perfomance instrumentation counters.

Orabug: 22607658

Signed-off-by: Dave Aldridge <david.j.aldridge@oracle.com>
(cherry picked from commit b0fb8b78a2cc452512296ce5bec1fa927ebf867e)
(cherry picked from commit da8cc212a978a1f54cadadeaabed46d9d5f839b3)
Signed-off-by: Allen Pais <allen.pais@oracle.com>