kunit/overflow: Fix UB in overflow_allocation_test

In the Linux kernel, the following vulnerability has been resolved: kunit/overflow: Fix UB in overflow_allocation_test The 'device_name' array doesn't exist out of the 'overflow_allocation_test' function scope. However, it is being used as a driver name when calling 'kunit_driver_create' from 'kunit_device_register'. It produces the kernel panic with KASAN enabled. Since this variable is used in one place only, remove it and pass the device name into kunit_device_register directly as an ascii string.