radv: fix computation of the number of user SGPRS for NGG GS state
The NGG GS state uses one user SGPR. Cc: 21.1 mesa-stable Signed-off-by:Samuel Pitoiset <samuel.pitoiset@gmail.com> Reviewed-by:
Timur Kristóf <timur.kristof@gmail.com> Part-of: <!10485>