tracing/uprobes: Fix to return -EFAULT if copy_from_user failed

Fix probe_mem_read() to return -EFAULT if copy_from_user()
failed. The copy_from_user() returns remaining bytes
when it failed, but probe_mem_read() caller expects it
returns error code like as probe_kernel_read().

Link: http://lkml.kernel.org/r/153547306719.26502.8353484532699160223.stgit@devbox

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_uprobe.c

@@ -105,7 +105,7 @@ probe_mem_read(void *dest, void *src, size_t size)
 {
 	void __user *vaddr = (void __force __user *)src;
 
-	return copy_from_user(dest, vaddr, size);
+	return copy_from_user(dest, vaddr, size) ? -EFAULT : 0;
 }
 /*
  * Fetch a null-terminated string. Caller MUST set *(u32 *)dest with max