ACPI: EC: Simplify locking in acpi_ec_event_handler()

Because acpi_ec_event_handler() is a work function, it always
runs in process context with interrupts enabled, so it can use
spin_lock_irq() and spin_unlock_irq() for the locking.

Make it do so and adjust white space around those calls.

No expected functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>