crypto: caam - fix invalid dereference in caam_rsa_init_tfm()

In case caam_jr_alloc() fails, ctx->dev carries the error code,
thus accessing it with dev_err() is incorrect.

Cc: <stable@vger.kernel.org> # 4.8+
Fixes: 8c419778 ("crypto: caam - add support for RSA algorithm")
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>