btrfs: cleanup, use kmalloc_array/kcalloc array helpers

Convert kmalloc(nr * size, ..) to kmalloc_array that does additional
overflow checks, the zeroing variant is kcalloc.

Signed-off-by: David Sterba <dsterba@suse.cz>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 9936421..8595fdd 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -578,7 +578,7 @@
 	if (!tree_mod_need_log(fs_info, eb))
 		return 0;
 
-	tm_list = kzalloc(nr_items * sizeof(struct tree_mod_elem *), flags);
+	tm_list = kcalloc(nr_items, sizeof(struct tree_mod_elem *), flags);
 	if (!tm_list)
 		return -ENOMEM;
 
@@ -677,7 +677,7 @@
 
 	if (log_removal && btrfs_header_level(old_root) > 0) {
 		nritems = btrfs_header_nritems(old_root);
-		tm_list = kzalloc(nritems * sizeof(struct tree_mod_elem *),
+		tm_list = kcalloc(nritems, sizeof(struct tree_mod_elem *),
 				  flags);
 		if (!tm_list) {
 			ret = -ENOMEM;
@@ -814,7 +814,7 @@
 	if (btrfs_header_level(dst) == 0 && btrfs_header_level(src) == 0)
 		return 0;
 
-	tm_list = kzalloc(nr_items * 2 * sizeof(struct tree_mod_elem *),
+	tm_list = kcalloc(nr_items * 2, sizeof(struct tree_mod_elem *),
 			  GFP_NOFS);
 	if (!tm_list)
 		return -ENOMEM;
@@ -905,8 +905,7 @@
 		return 0;
 
 	nritems = btrfs_header_nritems(eb);
-	tm_list = kzalloc(nritems * sizeof(struct tree_mod_elem *),
-			  GFP_NOFS);
+	tm_list = kcalloc(nritems, sizeof(struct tree_mod_elem *), GFP_NOFS);
 	if (!tm_list)
 		return -ENOMEM;