crypto: api - check for ERR pointers in crypto_destroy_tfm()

Given that crypto_alloc_tfm() may return ERR pointers, and to avoid
crashes on obscure error paths where such pointers are presented to
crypto_destroy_tfm() (such as [0]), add an ERR_PTR check there
before dereferencing the second argument as a struct crypto_tfm
pointer.

[0] https://lore.kernel.org/linux-crypto/000000000000de949705bc59e0f6@google.com/



Reported-by:  <syzbot+12cf5fbfdeba210a89dd@syzkaller.appspotmail.com>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>