scsi: lpfc: use monotonic timestamps for statistics

The get_seconds() function suffers from a possible overflow in 2038 or
2106, as well as jitter due to settimeofday or leap second updates, and is
deprecated.

As we are interested in elapsed time only, using ktime_get_seconds() to
read the CLOCK_MONOTONIC timebase is ideal here. This also lets us remove
the hack that tries to deal with get_seconds() going slightly backwards,
which cannot happen with montonic timestamps.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>