Replace 4 casts with 1
Replace 4 casts with 1

Changing the type of the |str| variable in asn1pars enables us to remove
4 casts with just 1. This silences an OpenBSD warning along the way.

RT4378

Reviewed-by: Richard Levitte <5fb523282dd7956571c80524edc2dccfa0bd8234@openssl.org>

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