IB/hfi1: Fix a wrapping test to insure the correct timeout

The "2 * UINT_MAX"  statement:
	if ((u64)(ts - cce->timestamp) > 2 * UINT_MAX) {

is equivalent to:
	if ((u64)(ts - cce->timestamp) > UINT_MAX - 1) {

This results in a premature timeout of the cong log entry.

Fix by using unsigned 64 bit integers, removing casts, and using
an algebraic equivalent test to avoid the "2 * UINT_MAX" issue.

Also make use of kernel API to get nanoseconds instead of
open coding.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/hfi1/mad.h

@@ -239,7 +239,7 @@ struct opa_hfi1_cong_log_event_internal {
 	u8 sl;
 	u8 svc_type;
 	u32 rlid;
-	s64 timestamp; /* wider than 32 bits to detect 32 bit rollover */
+	u64 timestamp; /* wider than 32 bits to detect 32 bit rollover */
 };
 
 struct opa_hfi1_cong_log_event {