HID: hid-lg4ff: Replace DEVICE_ATTR_RW with DEVICE_ATTR to have all internal functions prefixed with "lg4ff_"

Replace DEVICE_ATTR_RW with DEVICE_ATTR to have all internal functions prefixed
with "lg4ff_". All internal functions should be prefixed with just "lg4ff_".
Usage of DEVICE_ATTR_RW breaks this scheme because it expects the functions'
names to match the name of the respective sysfs entry.
This partially reverts "2f1cec32"
Signed-off-by: NMichal Malý <madcatxster@devoid-pointer.net>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>