mesa/st: Silence unused parameter warnings in st_context.c

src/mesa/state_tracker/st_context.c: In function ‘st_Enable’:
src/mesa/state_tracker/st_context.c:101:57: warning: unused parameter ‘state’ [-Wunused-parameter]
  101 | st_Enable(struct gl_context *ctx, GLenum cap, GLboolean state)
      |                                               ~~~~~~~~~~^~~~~

Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7167>
diff --git a/src/mesa/state_tracker/st_context.c b/src/mesa/state_tracker/st_context.c
index 2f45b65..68f5289 100644
--- a/src/mesa/state_tracker/st_context.c
+++ b/src/mesa/state_tracker/st_context.c
@@ -98,7 +98,7 @@
  * Called via ctx->Driver.Enable()
  */
 static void
-st_Enable(struct gl_context *ctx, GLenum cap, GLboolean state)
+st_Enable(struct gl_context *ctx, GLenum cap, UNUSED GLboolean state)
 {
    struct st_context *st = st_context(ctx);