ext4: Init the complete page while building buddy cache

We need to init the complete page during buddy cache init
by setting the contents to '1'.  Otherwise we can see the
following errors after doing an online resize of the
filesystem:

EXT4-fs error (device sdb1): ext4_mb_mark_diskspace_used:
	Allocating block 1040385 in system zone of 127 group
Signed-off-by: NAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
Cc: stable@kernel.org

fs/ext4/mballoc.c

@@ -846,6 +846,8 @@ static int ext4_mb_init_cache(struct page *page, char *incore)
 
 	err = 0;
 	first_block = page->index * blocks_per_page;
+	/* init the page  */
+	memset(page_address(page), 0xff, PAGE_CACHE_SIZE);
 	for (i = 0; i < blocks_per_page; i++) {
 		int group;
 		struct ext4_group_info *grinfo;
@@ -872,7 +874,6 @@ static int ext4_mb_init_cache(struct page *page, char *incore)
 			BUG_ON(incore == NULL);
 			mb_debug("put buddy for group %u in page %lu/%x\n",
 				group, page->index, i * blocksize);
-			memset(data, 0xff, blocksize);
 			grinfo = ext4_get_group_info(sb, group);
 			grinfo->bb_fragments = 0;
 			memset(grinfo->bb_counters, 0,