hfs: update timestamp on truncate()

hfs: update timestamp on truncate()

The vfs takes care of updating mtime on ftruncate(), but on truncate() it
must be done by the module.

Link: http://lkml.kernel.org/r/e1611eda2985b672ed2d8677350b4ad8c2d07e8a.1539316825.git.ernesto.mnd.fernandez@gmail.com
Signed-off-by: Ernesto A. Fernández <ernesto.mnd.fernandez@gmail.com>
Reviewed-by: Vyacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>