x86: Add return-value comment to cpu_jump_to_64bit()

This does not mention what it returns. Add the missing documentation.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/include/asm/cpu.h b/arch/x86/include/asm/cpu.h
index 3346012..073f80b 100644
--- a/arch/x86/include/asm/cpu.h
+++ b/arch/x86/include/asm/cpu.h
@@ -262,6 +262,7 @@
  *
  * @setup_base:	Pointer to the setup.bin information for the kernel
  * @target:	Pointer to the start of the kernel image
+ * Return: -EFAULT if the kernel returned; otherwise does not return
  */
 int cpu_jump_to_64bit(ulong setup_base, ulong target);