proc: fix /proc/*/pagemap some more

struct pagemap_walk was placed on stack, some hooks are initialized, the
rest (->pgd_entry, ->pud_entry, ->pte_entry) are valid but junk.

Reported-by: Eric Sesterhenn <snakebyte@gmx.de>
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: "Vegard Nossum" <vegard.nossum@gmail.com>
Cc: <stable@kernel.org> [2.6.25.x, 2.6.26.x]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 164bd9f..7546a91 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -636,7 +636,7 @@
 	struct pagemapread pm;
 	int pagecount;
 	int ret = -ESRCH;
-	struct mm_walk pagemap_walk;
+	struct mm_walk pagemap_walk = {};
 	unsigned long src;
 	unsigned long svpfn;
 	unsigned long start_vaddr;