fm10k: fix incorrect DIR_NEVATIVE bit in 1588 code

The SYSTIME_CFG.Adjust Direction bit is actually supposed to indicate
that the adjustment is positive. Fix the code to align correctly with
hardware and documentation.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <Krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>