avr32: Fix broken pte dump code in do_page_fault()

The per-task page tables only cover the first 2GiB of the address
space. For kernel addresses, we need to do the lookup in init's page
tables.

This is a temporary workaround until we modify the per-task page
tables to cover the whole 4GiB address space.

Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>