Input: adp5588-keys - use more obvious i2c_device_id name string

KBUILD_MODNAME normalizes "-" to "_".  This is non-obvious and results in
the id name for ADP5588 being "adp5588_keys" while the other supported id
is "adp5587-keys".  So avoid this define and use an explicit string as the
id name.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>