crypto: starfive - Do not free stack buffer

RSA text data uses variable length buffer allocated in software stack.
Calling kfree on it causes undefined behaviour in subsequent operations.

Cc: <stable@vger.kernel.org> #6.7+
Signed-off-by: Jia Jie Ho <jiajie.ho@starfivetech.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>