Build: correct assembler generation in crypto/rc4/build.info

In the removal of BEGINRAW / ENDRAW, attention to the difference
between capital .S and lowercase .s wasn't duly paid.  This corrects
the error.

Fixes #8155

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8157)