drm/qxl: remove unused `count` variable from `qxl_surface_id_alloc()`

Clang 14 in an (essentially) defconfig loongarch64 build for next-20240326
reports [1]:

drivers/gpu/drm/qxl/qxl_cmd.c:424:6: error: variable 'count' set
but not used [-Werror,-Wunused-but-set-variable]

The variable is already unused in the version that got into the tree.

Thus remove the unused variable.

Fixes: f64122c1f6ad ("drm: add new QXL driver. (v1.4)")
Closes: https://lore.kernel.org/lkml/[e-mail]/ [1]
Closes: https://lore.kernel.org/all/[e-mail]-3990X/
Signed-off-by: Miguel Ojeda <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Maxime Ripard <[e-mail]>

drivers/gpu/drm/qxl/qxl_cmd.c

···
 {
 	uint32_t handle;
 	int idr_ret;
-	int count = 0;
 again:
 	idr_preload(GFP_ATOMIC);
 	spin_lock(&qdev->surf_id_idr_lock);
···
 	handle = idr_ret;
 
 	if (handle >= qdev->rom->n_surfaces) {
-		count++;
 		spin_lock(&qdev->surf_id_idr_lock);
 		idr_remove(&qdev->surf_id_idr, handle);
 		spin_unlock(&qdev->surf_id_idr_lock);