drm: improve check for authentication.
drm: improve check for authentication.

On Linux systems, the drmGetClient() function would return the thread ID
instead of the actual process ID.

Signed-off-by: Gwenole Beauchesne <729713629d9640cc095f1c77c692e1881f8093c4@intel.com>

CyanogenMod/android_hardware_intel_libva,android-ia/hardware_intel_libva,halleyzhao/libva-fdo,halleyzhao/libva-fdo,android-ia/hardware_intel_libva,CyanogenMod/android_hardware_intel_libva,CyanogenMod/android_hardware_intel_libva,halleyzhao/libva-fdo,android-ia/hardware_intel_libva