soc: qcom: pil: Do not panic on powerup if the system is rebooting

When SSR occurs during reboot, ueventd may be killed which can cause
request_firmware in pil_boot to return an error. Do not panic in this
case as the request_firmware call is expected to fail.

Change-Id: I6bfdf4d9a634dec1aa56a1fdc5553cefe4a94a72
Signed-off-by: Kyle Yan <kyan@codeaurora.org>
Signed-off-by: Runmin Wang <runminw@codeaurora.org>