leds: qpnp-wled: improve OVP fault interrupt handling

If there is an OVP event happened in the bootloader and the
interrupt is not handled before, then as soon as the WLED
module is enabled, fault interrupt can fire. This is seen
sometimes during bootup. This is harmless as such and cannot
be stopped completely. However, it would be good to keep the
OVP fault interrupt disabled at the startup. When WLED module
is enabled again, it will get enabled anyways after ~10 ms.

While at it, print the error message in OVP fault interrupt
handler only when the fault status is set.

Change-Id: I0759c87137a52a8872b37d126e71c13f76d10e05
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>