nvc0: a geometry shader can have up to 1024 vertices output

The 1024 is already reported everywhere, not sure where this 0x1ff came
from.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "10.5 10.6" <mesa-stable@lists.freedesktop.org>

src/gallium/drivers/nouveau/nvc0/nvc0_program.c

@@ -392,7 +392,7 @@ nvc0_gp_gen_header(struct nvc0_program *gp, struct nv50_ir_prog_info *info)
       break;
    }
 
-   gp->hdr[4] = info->prop.gp.maxVertices & 0x1ff;
+   gp->hdr[4] = MIN2(info->prop.gp.maxVertices, 1024);
 
    return nvc0_vtgp_gen_header(gp, info);
 }