HID: hid-appletb-bl: use appletb_bl_brightness_map instead of magic numbers to...

HID: hid-appletb-bl: use appletb_bl_brightness_map instead of magic numbers to set default brightness

This commit makes use of appletb_bl_brightness_map instead of using if
statements and magic numbers to set default brightness, and thus simplifies
the code.

Signed-off-by: Aditya Garg <gargaditya08@live.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>