btrfs: switch to kcalloc in btrfs_cmp_data_prepare

Kcalloc is functionally equivalent and does overflow checks.

Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 55440a7..11dae2a 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2925,8 +2925,8 @@
 	 * of the array is bounded by len, which is in turn bounded by
 	 * BTRFS_MAX_DEDUPE_LEN.
 	 */
-	src_pgarr = kzalloc(num_pages * sizeof(struct page *), GFP_KERNEL);
-	dst_pgarr = kzalloc(num_pages * sizeof(struct page *), GFP_KERNEL);
+	src_pgarr = kcalloc(num_pages, sizeof(struct page *), GFP_KERNEL);
+	dst_pgarr = kcalloc(num_pages, sizeof(struct page *), GFP_KERNEL);
 	if (!src_pgarr || !dst_pgarr) {
 		kfree(src_pgarr);
 		kfree(dst_pgarr);