ibmvmc: update ctime in conjunction with mtime on 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..."

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Message-Id: <20230705190309.579783-1-jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>