Replace lp5521/5523_unregister_sysfs() with lp55xx_unregister_sysfs().

 On unloading the driver, running engines should be stopped.
 Use explicit driver function, lp5521/5523_stop_engine().

 Unused functions are removed.
Signed-off-by: NMilo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: NBryan Wu <cooloney@gmail.com>