cpufreq: imx6q: Fix handling EPROBE_DEFER from regulator

If there are any errors in getting the cpu0 regulators, the driver returns
-ENOENT. In case the regulators are not yet available, the devm_regulator_get
calls will return -EPROBE_DEFER, so that the driver can be probed later.
If we return -ENOENT, the driver will fail its initialization and will
not try to probe again (when the regulators become available).

Return the actual error received from regulator_get in probe. Print a
differentiated message in case we need to probe the device later and
in case we actually failed. Also add a message to inform when the
driver has been successfully registered.

Signed-off-by: Irina Tirdea <irina.tirdea@nxp.com>
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>