crypto: fix gcrypt min version 1.8 regression

crypto: fix gcrypt min version 1.8 regression

The min gcrypt was bumped:

  commit b33a84632a3759c00320fd80923aa963c11207fc
  Author: Daniel P. Berrangé <berrange@redhat.com>
  Date:   Fri May 14 13:04:08 2021 +0100

    crypto: bump min gcrypt to 1.8.0, dropping RHEL-7 support

but this was accidentally lost in conflict resolution for

  commit 5761251138cb69c310e9df7dfc82c4c6fd2444e4
  Author: Paolo Bonzini <pbonzini@redhat.com>
  Date:   Thu Jun 3 11:15:26 2021 +0200

    configure, meson: convert crypto detection to meson

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>