[POWERPC][XEN] Fix uninitialized variable warning.

Signed-off-by: Hollis Blanchard <hollisb@us.ibm.com>

--HG--
extra : transplant_source : %EA%0C%00o%AA%B6%8D%2C%2Aeu%0C%90%EC%88%81%F0%E0%B0%03

xen/arch/powerpc/memory.c

@@ -120,7 +120,7 @@ void memory_init(module_t *mod, int mcount)
 {
     ulong eomem;
     ulong bitmap_start = ~0UL;
-    ulong bitmap_end;
+    ulong bitmap_end = 0;
     ulong bitmap_size;
     ulong xh_pages;
     ulong start;