USB-PD: Don't make charge_manager save log if it's not present

Currently, pd_log assumes charge manager exists, thus, build fails
if CONFIG_CHARGE_MANAGER is undefined because charge_manager_save_log
is missing. This patch fixes it.

Signed-off-by: Daisuke Nojiri <dnojiri@chromium.org>

BUG=none
BRANCH=none
TEST=buildall

Change-Id: I36156e7b376717a53e8a2cab7483b5150b4f2d61
Reviewed-on: https://chromium-review.googlesource.com/1300615
Commit-Ready: Daisuke Nojiri <dnojiri@chromium.org>
Tested-by: Daisuke Nojiri <dnojiri@chromium.org>
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>
1 file changed