powerpc: fix skipping call to early_init_fdt_scan_reserved_mem

The call to early_init_fdt_scan_reserved_mem will be skipped if
reserved-ranges is not found. Move the call earlier so that it is called
unconditionally.

Signed-off-by: Rob Herring <robh@kernel.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: linuxppc-dev@lists.ozlabs.org
Tested-by: Stephen Chivers <schivers@csc.com>