radeonsi: set num_input_vgprs for fragment shaders in create_function
radeonsi: set num_input_vgprs for fragment shaders in create_function

So that the prolog generated for monolithic fragment shaders will have the
right signature.

Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler