msm: ep_pcie: fix the bug in debugfs testing

PCIe device ID can't be got from register when the power of the
core is off. Thus, use the saved device ID so that we can turn on
link in the debugfs testing.

Change-Id: I28ec17b4fdf84b130cd32267d097b1c0d7c32aed
Signed-off-by: Yan He <yanhe@codeaurora.org>