crypto: ecdsa - Rename keylen to bufsize where necessary

[ Upstream commit 703ca5cd ]

In cases where 'keylen' was referring to the size of the buffer used by
a curve's digits, it does not reflect the purpose of the variable anymore
once NIST P521 is used. What it refers to then is the size of the buffer,
which may be a few bytes larger than the size a coordinate of a key.
Therefore, rename keylen to bufsize where appropriate.

Tested-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Stable-dep-of: 3b0565c7 ("crypto: ecdsa - Avoid signed integer overflow on signature decoding")
Signed-off-by: Sasha Levin <sashal@kernel.org>