MIPS: kernel: Fix for_each_memblock conversion

The loop over all memblocks works with PFNs and not physical
addresses, so we need for_each_mem_pfn_range().

Fixes: b10d6bca ("arch, drivers: replace for_each_membock() with for_each_mem_range()")
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>