libcgc: subreg can be zero

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
libcgc: there seems to be one more significant bit here

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
libcgc: these seem to be pipeline registers

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>