cyclic: stop strdup'ing name in cyclic_register()

We are not checking the return value of strdup(), nor
freeing the string in cyclic_unregister().

However, all current users either pass a string literal or the
dev->name of the client device. So in all cases the name string will
live at least as long as the cyclic_info is registered, so just make
that a requirement.

Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>