fs/ntfs: use timespec64 directly for timestamp conversion

Now that the VFS has been converted from timespec to timespec64
timestamps, only the conversion to/from ntfs timestamps uses 32-bit
seconds.

This changes that last missing piece to get the ntfs implementation
y2038 safe on 32-bit architectures.

Link: http://lkml.kernel.org/r/20180718115017.742609-2-arnd@arndb.de


Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Anton Altaparmakov <anton@tuxera.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>