regulator: cpr-regulator: change CPR debug message level for OPP table

Change the CPR debug message level from error to debug if filling the
OPP table failed. This is to avoid logging the error messages on the
platforms which do not have pm_opp enabled.

Change-Id: I430ae7a38ae41ade8e7b94346f6fda77e8f5cb9c
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>