Input: axp20x-pek - make device attributes static

Input: axp20x-pek - make device attributes static

The two device attrbitues are not declared outside this file
so make them static to avoid the following warnings:

drivers/input/misc/axp20x-pek.c:194:1: warning: symbol 'dev_attr_startup' was not declared. Should it be static?
drivers/input/misc/axp20x-pek.c:195:1: warning: symbol 'dev_attr_shutdown' was not declared. Should it be static?

Signed-off-by: Ben Dooks (Codethink) <ben.dooks@codethink.co.uk>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Link: https://lore.kernel.org/r/20191217152541.2167080-1-ben.dooks@codethink.co.uk
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>