HID: amd_sfh: Fix illuminance value

Illuminance value is actually 32 bits, but is incorrectly trancated to
16 bits. Hence convert to integer illuminace accordingly to reflect
correct values.

Fixes: 93ce5e02 ("HID: amd_sfh: Implement SFH1.1 functionality")
Signed-off-by: Basavaraj Natikar <Basavaraj.Natikar@amd.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>