drm/i915: Replace kmalloc() + copy_from_user() with memdup_user()

Replace kmalloc() followed by copy_from_user() with memdup_user() to
improve and simplify set_context_image(), and to silence the following
Coccinelle/coccicheck warning reported by memdup_user.cocci:

  WARNING opportunity for memdup_user

No functional changes intended.

Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Tvrtko Ursulin <tursulin@ursulin.net>
Link: https://lore.kernel.org/r/20250902081046.35463-2-thorsten.blum@linux.dev

Author: toblux

drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -2158,18 +2158,12 @@ static int set_context_image(struct i915_gem_context *ctx,
 		goto out_ce;
 	}
 
-	state = kmalloc(ce->engine->context_size, GFP_KERNEL);
-	if (!state) {
-		ret = -ENOMEM;
+	state = memdup_user(u64_to_user_ptr(user.image), ce->engine->context_size);
+	if (IS_ERR(state)) {
+		ret = PTR_ERR(state);
 		goto out_ce;
 	}
 
-	if (copy_from_user(state, u64_to_user_ptr(user.image),
-			   ce->engine->context_size)) {
-		ret = -EFAULT;
-		goto out_state;
-	}
-
 	shmem_state = shmem_create_from_data(ce->engine->name,
 					     state, ce->engine->context_size);
 	if (IS_ERR(shmem_state)) {