RDMA/ucma: Convert open-coded equivalent to memdup_user()

Suggested by scripts/coccinelle/api/memdup_user.cocci.
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>

drivers/infiniband/core/ucma.c

@@ -1002,23 +1002,18 @@ static ssize_t ucma_set_option(struct ucma_file *file, const char __user *inbuf,
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
 
-	optval = kmalloc(cmd.optlen, GFP_KERNEL);
-	if (!optval) {
-		ret = -ENOMEM;
-		goto out1;
-	}
-
-	if (copy_from_user(optval, (void __user *) (unsigned long) cmd.optval,
-			   cmd.optlen)) {
-		ret = -EFAULT;
-		goto out2;
+	optval = memdup_user((void __user *) (unsigned long) cmd.optval,
+			     cmd.optlen);
+	if (IS_ERR(optval)) {
+		ret = PTR_ERR(optval);
+		goto out;
 	}
 
 	ret = ucma_set_option_level(ctx, cmd.level, cmd.optname, optval,
 				    cmd.optlen);
-out2:
 	kfree(optval);
-out1:
+
+out:
 	ucma_put_ctx(ctx);
 	return ret;
 }