Update RAND_DRBG.pod
Update RAND_DRBG.pod

Fixed a minor typo while reading the documentation.
I agree that this contribution is trivial can be freely used.

CLA: trivial

Reviewed-by: Nicola Tuveri <5a38b4ac03c90be61ead22c1d11b6e9f49425984@gmail.com>
Reviewed-by: Kurt Roeckx <bb87b47479d83cec3c76132206933257ded727b2@roeckx.be>
(Merged from https://github.com/openssl/openssl/pull/7221)

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