As additional clarification if needed, if your character wanted "use magical device" for some reason, it would have a max of 5 ranks, since it is an exclusive skill for rogues (and bards).
OT: one of the best reasons for a wizard to start with a level of rogue is not for the extra skill points at 1st level, but for the better skill caps for cross-class skills which are on the rogue list.
a Rog1/Wiz 11 could have +15 spot, while the Wiz 12 could only have +7. Wizards tend to have lots of extra skill points from their high INT, and this gives them the chance to specialise in a particularly useful skill. (The idea of a Rog1/Wiz11 with +15 tumble is quite an interesting one. I bet that would take his opponents by surprise!)
Cheers