ppdev: fix PPGETTIME/PPSETTIME ioctls

ppdev: fix PPGETTIME/PPSETTIME ioctls

Going through the uses of timeval in the user space API,
I noticed two bugs in ppdev that were introduced in the y2038
conversion:

* The range check was accidentally moved from ppsettime to
  ppgettime

* On sparc64, the microseconds are in the other half of the
  64-bit word.

Fix both, and mark the fix for stable backports.

Cc: stable@vger.kernel.org
Fixes: 3b9ab374a1e6 ("ppdev: convert to y2038 safe")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20191108203435.112759-8-arnd@arndb.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>