x86: fsp: Simplify fsp_continue()

There is no need to pass shared_data to fsp_continue() so we can
remove unnecessary codes that simplifies the function a lot.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>