crypto: essiv - remove redundant null pointer check before kfree

[ Upstream commit e18036da5c23530994faf7243b592e581f1efed2 ]

kfree has taken null pointer check into account. so it is safe to
remove the unnecessary check.

Signed-off-by: Chen Wandun <chenwandun@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Stable-dep-of: b5a772adf45a ("crypto: essiv - Handle EBUSY correctly")
Signed-off-by: Sasha Levin <sashal@kernel.org>