ata: fix "ering" sysfs time printing

The sysfs file for the libata error handling has multiple issues
in the way it prints time stamps:

 * it prints a 9-digit nanosecond value using a %06lu format string,
   which drops some leading zeroes
 * it converts a 64-bit jiffes value to a timespec using
   jiffies_to_timespec(), which takes a 'long' argument, so the
   result is wrong after a jiffies overflow (49 days).
 * we try to avoid using timespec because that generally overflows
   in 2038, although this particular usage is ok.

This replaces the jiffies_to_timespec call with an open-coded
implementation that gets it right.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Tejun Heo <tj@kernel.org>