x86/uv: Fix the UV BAU destination timeout period

x86/uv: Fix the UV BAU destination timeout period

Correct the calculation of a destination timeout period, which
is used to distinguish between a destination timeout and the
situation where all the target software ack resources are full
and a request is returned immediately.

The problem is that integer arithmetic was overflowing, yielding
a very large result.

Without this fix destination timeouts are identified as resource
'plugged' events and an ipi method of resource releasing is
unnecessarily employed.

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Link: http://lkml.kernel.org/r/20120622131212.GA31884@sgi.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>