program: Use _mesa_geometric_samples to calculate gl_NumSamples
program: Use _mesa_geometric_samples to calculate gl_NumSamples

Otherwise it won't take into account the default samples for
framebuffers with no attachments.

Reviewed-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler