drivers: platform: change 0x20 to I8042_STR_AUXDATA in i8042 filters

Instead of using a magic constant 0x20 in some drivers to get data only
from the KBC port we should use the constant defined in i8042.h with
the same value. Also, this makes these drivers uniform with what
constant the only other filter function uses in
drivers/input/misc/ideapad_slidebar.c.

Signed-off-by: Giedrius Statkevičius <giedriuswork@gmail.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>