gcrypt: Bugfix for very slow ecdh

Signed-off-by: Aris Adamantiadis <aris@0xbadc0de.be>
Reviewed-by: Jakub Jelen <jjelen@redhat.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>
(cherry picked from commit 9546b20dec8ebe1896fb5a5c6ed6b7d5f9dc8b0c)