GPU-DRM-Savage: Use memdup_user() rather than duplicating

Reuse existing functionality from memdup_user() instead of keeping
duplicate source code.

This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/021efa32-c259-e799-a80e-630972291815@users.sourceforge.net

drivers/gpu/drm/savage/savage_state.c

@@ -1001,15 +1001,9 @@ int savage_bci_cmdbuf(struct drm_device *dev, void *data, struct drm_file *file_
 		cmdbuf->cmd_addr = kcmd_addr;
 	}
 	if (cmdbuf->vb_size) {
-		kvb_addr = kmalloc(cmdbuf->vb_size, GFP_KERNEL);
-		if (kvb_addr == NULL) {
-			ret = -ENOMEM;
-			goto done;
-		}
-
-		if (copy_from_user(kvb_addr, cmdbuf->vb_addr,
-				       cmdbuf->vb_size)) {
-			ret = -EFAULT;
+		kvb_addr = memdup_user(cmdbuf->vb_addr, cmdbuf->vb_size);
+		if (IS_ERR(kvb_addr)) {
+			ret = PTR_ERR(kvb_addr);
 			goto done;
 		}
 		cmdbuf->vb_addr = kvb_addr;