Documentation: qat: change kernel version

Change kernel version from 5.20 to 6.0, as 5.20 is not a release.

Signed-off-by: Meadhbh Fitzpatrick <meadhbh.fitzpatrick@intel.com>
Reviewed-by: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
Reviewed-by: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>