mproved EAS candidate fallback behavior in select_cpu_candidates() so we no longer pre-seed highest_spare_cap_cpu with prev_cpu; this prevents carrying an ineligible fallback CPU into the final candidate mask on big.LITTLE/EAS paths.

Updated spare-capacity selection to “first valid CPU or best spare CPU” semantics (|| ... < 0) for both per-performance-domain and prefer-idle non-idle fallback tracking, so a valid candidate is still selected even when spare capacity is zero.

Guarded the final fallback cpumask_set_cpu() with highest_spare_cap_cpu >= 0, avoiding insertion of an invalid CPU when no candidate passed filters.

Signed-off-by: The_Anomalist