power: supply: qpnp-smblite: only enable WDOG during USB plugin

WDOG_TIMER_EN_BIT is used for enabling WDOG all the time, this is not
required hence remove it.

Change-Id: I68ffff4dd3e3fdc669cb7a45948fd308107d81ad
Signed-off-by: Fenglin Wu <fenglinw@codeaurora.org>