fat: propagate 64-bit inode timestamps

Now that we pass down 64-bit timestamps from VFS, we just need to convert
that correctly into on-disk timestamps.  To make that work correctly, this
changes the last use of time_to_tm() in the kernel to time64_to_tm(),
which also lets use remove that deprecated interfaces.

Similarly, the time_t use in fat_time_fat2unix() truncates the timestamp
on the way in, which can be avoided by using types that are wide enough to
hold the intermediate values during the conversion.

[hirofumi@mail.parknet.co.jp: remove useless temporary variable, needless long long]
Link: http://lkml.kernel.org/r/20180619153646.3637529-1-arnd@arndb.de


Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>