cpuidle: Warn instead of bailing out if target residency check fails

cpuidle: Warn instead of bailing out if target residency check fails

It turns out that the change in commit 76934e495cdc ("cpuidle: Add
sanity check for exit latency and target residency") goes too far
because there are systems in the field on which the check introduced
by that commit does not pass.

For this reason, change __cpuidle_driver_init() return type back to void
and make it print a warning when the check mentioned above does not
pass.

Fixes: 76934e495cdc ("cpuidle: Add sanity check for exit latency and target residency")
Reported-by: Val Packett <val@packett.cool>
Closes: https://lore.kernel.org/linux-pm/20251121010756.6687-1-val@packett.cool/
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/2808566.mvXUDI8C0e@rafael.j.wysocki