Fix clearkey return code for setSecurityLevel

When passing an invalid security level to
DrmPlugin::setSecurityLevel, an incorrect error code
was being returned, based on the drm@1.1 DrmPlugin.hal
documentation. This CL corrects the error code.

Change-Id: If560be07f3945320d28c42cb2cf18d8f8c718229
related-to-bug:73330999
bug:77308498
Test:VtsHalDrmV1_1Target