mmtimer: add member name to the miscdevice declaration

Since the struct miscdevice have many members, it is dangerous to init
it without members name relying only on member order.

This patch add member name to the init declaration.

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>