svga: add switch cases for PIPE_SHADER_CAP_OUTPUT_READ

Silences unhandled switch case warning.
Return 0 since we don't want to read from output regs.

src/gallium/drivers/svga/svga_screen.c

@@ -259,6 +259,8 @@ static int svga_get_shader_param(struct pipe_screen *screen, unsigned shader, en
          return 0;
       case PIPE_SHADER_CAP_MAX_TEXTURE_SAMPLERS:
          return 16;
+      case PIPE_SHADER_CAP_OUTPUT_READ:
+         return 0;
       }
       break;
    case PIPE_SHADER_VERTEX:
@@ -302,6 +304,8 @@ static int svga_get_shader_param(struct pipe_screen *screen, unsigned shader, en
          return 0;
       case PIPE_SHADER_CAP_INTEGERS:
          return 0;
+      case PIPE_SHADER_CAP_OUTPUT_READ:
+         return 0;
       default:
          break;
       }