crypto: kpp - Add helper to set reqsize

[ Upstream commit 56861cbd ]

The value of reqsize should only be changed through a helper.
To do so we need to first add a helper for this.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Stable-dep-of: eb7713f5 ("crypto: qat - unmap buffer before free for DH")
Signed-off-by: Sasha Levin <sashal@kernel.org>