[PATCH] powerpc: Another maple merge tree fix

With ARCH=powerpc, a spurious ifdef in prom_init prevented the
seconday hold loop being correctly copied down on Maple.  With this
patch, Maple boots with ARCH=powerpc

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>