rpmsg: char: release allocated memory

In rpmsg_eptdev_write_iter, if copy_from_iter_full fails the allocated
buffer needs to be released.

Signed-off-by: Navid Emamdoost <[e-mail]>
Signed-off-by: Bjorn Andersson <[e-mail]>

drivers/rpmsg/rpmsg_char.c

···
 	if (!kbuf)
 		return -ENOMEM;
 
-	if (!copy_from_iter_full(kbuf, len, from))
-		return -EFAULT;
+	if (!copy_from_iter_full(kbuf, len, from)) {
+		ret = -EFAULT;
+		goto free_kbuf;
+	}
 
 	if (mutex_lock_interruptible(&eptdev->ept_lock)) {
 		ret = -ERESTARTSYS;