infiniband: cxgb4: use ktime_get for timestamps

infiniband: cxgb4: use ktime_get for timestamps

The debugfs file prints the difference between host timestamps as a
seconds/nanoseconds tuple, along with a 64-bit nanoseconds hardware
timestamp. The host time is read using getnstimeofday() which is
deprecated because of the y2038 overflow, and it suffers from time jumps
during settimeofday() and leap seconds.

Converting to ktime_get_ts64() would solve those two, but I'm going
a little further here by changing to ktime_get() and printing 64-bit
nanoseconds on both host and hw timestamps.  This simplifies the code
further and makes the output easier to understand.

The format of the debugfs file obviously changes here, but this should
only be read by humans and not scripts, so I assume it's fine.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Steve Wise <swise@opengridcomputing.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>