fs: affs: Initialize filesystem timestamp ranges

Fill in the appropriate limits to avoid inconsistencies
in the vfs cached inode times when timestamps are
outside the permitted range.

Also fix timestamp calculation to avoid overflow
while converting from days to seconds.

Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Acked-by: David Sterba <dsterba@suse.com>
Acked-by: Jeff Layton <jlayton@kernel.org>
Cc: dsterba@suse.com