btrfs: Replace kmalloc with kmalloc_array

Replace kmalloc(size * nr, ) with kmalloc_array(nr, size), thus making
it easier to check is that the calculation doesn't wrap or return a smaller allocation

Signed-off-by: Dulshani Gunawardhana <dulshani.gunawardhana89@gmail.com>
Reviewed-by: Zach Brown <zab@redhat.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index c9079db..1de6d4d 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1470,7 +1470,7 @@
 	nr_devices = fs_info->fs_devices->open_devices;
 	BUG_ON(!nr_devices);
 
-	devices_info = kmalloc(sizeof(*devices_info) * nr_devices,
+	devices_info = kmalloc_array(nr_devices, sizeof(*devices_info),
 			       GFP_NOFS);
 	if (!devices_info)
 		return -ENOMEM;