drm/panthor: Fix clang -Wunused-but-set-variable in tick_ctx_apply()

Clang warns (or errors with CONFIG_WERROR):

  drivers/gpu/drm/panthor/panthor_sched.c:2048:6: error: variable 'csg_mod_mask' set but not used [-Werror,-Wunused-but-set-variable]
   2048 |         u32 csg_mod_mask = 0, free_csg_slots = 0;
        |             ^
  1 error generated.

The variable is an artifact left over from refactoring that occurred
during the development of the initial series for this driver. Remove it
to resolve the warning.

Fixes: de854881 ("drm/panthor: Add the scheduler logical block")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Justin Stitt <justinstitt@google.com>
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240328-panthor-drop-csg_mod_mask-v1-1-5a80be3df581@kernel.org

drivers/gpu/drm/panthor/panthor_sched.c

@@ -2045,7 +2045,7 @@ tick_ctx_apply(struct panthor_scheduler *sched, struct panthor_sched_tick_ctx *c
 	struct panthor_device *ptdev = sched->ptdev;
 	struct panthor_csg_slot *csg_slot;
 	int prio, new_csg_prio = MAX_CSG_PRIO, i;
-	u32 csg_mod_mask = 0, free_csg_slots = 0;
+	u32 free_csg_slots = 0;
 	struct panthor_csg_slots_upd_ctx upd_ctx;
 	int ret;
 
@@ -2139,7 +2139,6 @@ tick_ctx_apply(struct panthor_scheduler *sched, struct panthor_sched_tick_ctx *c
 
 			csg_iface = panthor_fw_get_csg_iface(ptdev, csg_id);
 			csg_slot = &sched->csg_slots[csg_id];
-			csg_mod_mask |= BIT(csg_id);
 			group_bind_locked(group, csg_id);
 			csg_slot_prog_locked(ptdev, csg_id, new_csg_prio--);
 			csgs_upd_ctx_queue_reqs(ptdev, &upd_ctx, csg_id,