ext4: use kmemdup() to replace kmalloc + memcpy

ext4: use kmemdup() to replace kmalloc + memcpy

[ Upstream commit ab3af306998e1b050dd3ec91294b50e523c9ad1f ]

Replace kmalloc + memcpy with kmemdup()

Signed-off-by: Shuqi Zhang <zhangshuqi3@huawei.com>
Reviewed-by: Ritesh Harjani <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20220525030120.803330-1-zhangshuqi3@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Stable-dep-of: 246b6193fbe5 ("ext4: fix deadlock due to mbcache entry corruption")
Signed-off-by: Sasha Levin <sashal@kernel.org>