mei/hdcp: Fix SPDX identifiers

1. Remove redundant parentheses around single license
2. Fix the license to GPL-2.0 and not GPL-2.0+ in mei_hdcp.h

Cc: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>