leds: leds-qpnp: remove the usage of mutex_destroy for static mutex

Remove the call to mutex_destroy for the statically defined
mutex flash_lock.

CRs-Fixed: 640712
Change-Id: I664b0b94ff8e2f74d49d3f759d955bee513e5daf
Signed-off-by: Abinaya P <abinayap@codeaurora.org>