rsa/rsa_ossl.c: fix and extend commentary [skip ci].
rsa/rsa_ossl.c: fix and extend commentary [skip ci].

Reviewed-by: Richard Levitte <5fb523282dd7956571c80524edc2dccfa0bd8234@openssl.org>
Reviewed-by: Nicola Tuveri <5a38b4ac03c90be61ead22c1d11b6e9f49425984@gmail.com>
(Merged from https://github.com/openssl/openssl/pull/7123)

openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl,openssl/openssl