HID: input: map battery capacity (00850065)

This is the capacity in percentage, relative to design capacity.
Specifically, it is present in Apple Magic Mouse 2.

In contrast, usage 00850064 is also the capacity in percentage, but is
relative to full capacity. It is not mapped here because I don't have
such device.

Signed-off-by: John Chen <johnchen902@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>