mfd: atmel-flexcom: Remove #ifdef CONFIG_PM_SLEEP

Remove compilation flag and use __maybe_unused and pm_ptr instead.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20211028135138.3481166-2-claudiu.beznea@microchip.com