soc: pil-q6v5: Set the optimum current before disabling vreg_pll

In the cases where the regulator is always on, the RPM checks the
current requirement to put it into a low-power-mode. Set the
optimum requirement to 0 before disabling the regulator.

Change-Id: Icea5d0a81da5539bb5130022a92195af4c6f2eb5
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>