leds: leds-qpnp-wled: set overwrite bit for switching frequency

While configuring the switching frequency for WLED, we need to set
the overwrite bit as well so that the switching frequency change
will get reflected.

Change-Id: I3e7f67b76ac49c1d925a8e84ea1280160ee044bd
Signed-off-by: Abinaya P <abinayap@codeaurora.org>