HID: hid-input: fix stylus battery reporting

HID: hid-input: fix stylus battery reporting

With commit 4f3882177240 hid-input started clearing of "ignored" usages
to avoid using garbage that might have been left in them. However
"battery strength" usages should not be ignored, as we do want to
use them.

Fixes: 4f3882177240 ("HID: hid-input: clear unmapped usages")
Reported-by: Kenneth Albanowski <kenalba@google.com>
Tested-by: Kenneth Albanowski <kenalba@google.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>