[PATCH] powerpc: Fix search for the main interrupt controller

At present, we are not looking at all interrupt controller nodes in the
device tree even though the proper node was not found. This is causing
the system panic. The attached patch will scan all nodes until it finds
the proper interrupt controller type.

Signed-off-by: Haren Myneni <haren@us.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>