drm/i915/hdcp: Fix the return handling of drm_hdcp_check_ksvs_revoked

drm_hdcp_check_ksvs_revoked() returns the number of revoked keys and
error codes when the SRM parsing is failed.

Errors in SRM parsing can't affect the HDCP auth, hence with this patch,
I915 will look out for revoked key count alone.

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
cc: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Sean Paul <sean@poorly.run>
Link: https://patchwork.freedesktop.org/patch/msgid/20200429134555.22106-1-ramalingam.c@intel.com