Input: adp5588-keys - use new PM macros

With the new PM macros (DEFINE_SIMPLE_DEV_PM_OPS() and pm_sleep_ptr()), the
compiler has visibility to see that the functions are not used when
!CONFIG_PM and hence, remove the dead code. As such, there's no need
for '__maybe_unused'.

Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20220829131553.690063-11-nuno.sa@analog.com


Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>