leds: lp5521/5523: Remove duplicate mutex

leds: lp5521/5523: Remove duplicate mutex

It can be a problem when a pattern is loaded via the firmware interface.
LP55xx common driver has already locked the mutex in 'lp55xx_firmware_loaded()'.
So it should be deleted.

On the other hand, locks are required in store_engine_load()
on updating program memory.

Reported-by: Pali Rohár <[email protected]>
Reported-by: Pavel Machek <[email protected]>
Signed-off-by: Milo Kim <[email protected]>
Signed-off-by: Bryan Wu <[email protected]>
Cc: <[email protected]>