fat: truncate inode timestamp updates in setattr

setattr_copy can't truncate timestamps correctly for
msdos/vfat, so truncate and copy them ourselves.

Link: http://lkml.kernel.org/r/a2b4701b1125573fafaeaae6802050ca86d6f8cc.1538363961.git.sorenson@redhat.com


Signed-off-by: Frank Sorenson <sorenson@redhat.com>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>