Fix typo in comment
Fix typo in comment

The one in rsa.c was overlooked when fixing the same comment in
pkey.c as part of eff1752b66cb7bf6ca8af816eb10ead26910d025.

Reviewed-by: Rich Salz <c04971a99e5a9ee80eaab4b1deb37e845b0bd697@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4902)

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