fs: cifs: Delete usage of timespec64_trunc

timestamp_truncate() is the replacement api for
timespec64_trunc. timestamp_truncate() additionally clamps
timestamps to make sure the timestamps lie within the
permitted range for the filesystem.

Truncate the timestamps in the struct cifs_attr at the
site of assignment to inode times. This
helps us use the right fs api timestamp_trucate() to
perform the truncation.

Also update the ktime_get_* api to match the one used in
current_time(). This allows for timestamps to be updated
the same way always.

Signed-off-by: Deepa Dinamani <deepa.kernel@gmail.com>
Cc: stfrench@microsoft.com
Cc: linux-cifs@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>