Pass Device object when setting up Dialog_Partition_New (#746214)

Adding a partition name entry to the Create New Partition dialog will
need access to these two Device methods: partition_naming_supported()
and get_max_partition_length().  The Set_Data() function already takes
two parameters, only_unformatted and disktype, taken from Device member
variables.

Rather than add two more parameters to the Set_Data() function pass the
Device object instead, replacing the current only_unformatted and
disktype parameters.

Bug 746214 - Partition name enhancements