ARM: cpuidle: Don't register the driver when back-end init returns -ENXIO

There's no point to register the cpuidle driver for the current CPU, when
the initialization of the arch specific back-end data fails by returning
-ENXIO.

Instead, let's re-order the sequence to its original flow, by first trying
to initialize the back-end part and then act accordingly on the returned
error code. Additionally, let's print the error message, no matter of what
error code that was returned.

Fixes: a0d46a3d (ARM: cpuidle: Register per cpuidle device)
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: 4.19+ <stable@vger.kernel.org> # v4.19+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>