powerpc: Fix assmption of end_of_DRAM() returns end address

memblock_end_of_DRAM() returns end_address + 1, not end address.
While some code assumes that it returns end address.

Signed-off-by: Bharat Bhushan <bharat.bhushan@freescale.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>