drm/i915/hdcp: require monotonically increasing seq_num_v

drm/i915/hdcp: require monotonically increasing seq_num_v

The HDCP 2.2 specification requires the seq_num_v to be monotonically
increasing, and repeated seq_num_v needs to be treated as an integrity
failure. Make it so.

For the first message, seq_num_v must be zero, and is already
checked. We can only check for less-than-or-equal for the subsequent
messages, where hdcp2_encrypted is true.

Discovered using AI-assisted static analysis confirmed by Intel Product
Security.

Reported-by: Martin Hodo <martin.hodo@intel.com>
Fixes: d849178e2c9e ("drm/i915: Implement HDCP2.2 repeater authentication")
Cc: stable@vger.kernel.org # v5.2+
Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patch.msgid.link/20260625104407.1025614-1-jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
(cherry picked from commit 58a224375c81179b52558c53d8857b93196d2687)
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>