[PATCH] powerpc: fix uninitialised error in numa.c

chroma_defconfig currently gives me this with gcc 4.6:
  arch/powerpc/mm/numa.c:638:13: error: 'dm' may be used uninitialized in this function [-Werror=uninitialized]

It's a bogus warning since of_get_drconf_memory() only writes it
anyway.  

Signed-off-by: Michael Neuling <redacted>
cc: stable@kernel.org
---
Also affects 3.4 and 3.3 stable.

diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
index 5ca3a15..880acde 100644
--- a/arch/powerpc/mm/numa.c
+++ b/arch/powerpc/mm/numa.c

@@ -637,7 +637,7 @@ static inline int __init read_usm_ranges(const u32 **usm)
  */
 static void __init parse_drconf_memory(struct device_node *memory)
 {
-	const u32 *dm, *usm;
+	const u32 *dm = NULL, *usm;
 	unsigned int n, rc, ranges, is_kexec_kdump = 0;
 	unsigned long lmb_size, base, size, sz;
 	int nid;