cifs: update the ctime on a partial page write

POSIX says:

    "Upon successful completion, where nbyte is greater than 0, write()
     shall mark for update the last data modification and last file status
     change timestamps of the file..."

Add the missing ctime update.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Steve French <stfrench@microsoft.com>
Message-Id: <20230705190309.579783-6-jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>