drm/hdcp: fix DRM_HDCP_2_KSV_COUNT_2_LSBITS

Need to extract the 2 most significant bits from a byte for constructing
the revoked KSV count of the SRM.

Signed-off-by: Ramalingam C <ramalingam.c@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200212102942.26568-3-ramalingam.c@intel.com