Fix coverity CID #1466378 - Incorrect expression in ec_backend.c
Fix coverity CID #1466378 - Incorrect expression in ec_backend.c

Reviewed-by: Matthias St. Pierre <1910231d24f125aceac7850dc92279eee8d52323@ncp-e.com>
(Merged from https://github.com/openssl/openssl/pull/12708)

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