ARM: dts: msm: remove VBAT_WEAK configuration

VBAT_WEAK gets updated based on adaptive boot. Restrict
any update of VBAT_WEAK register driver by removing it's
configuration entry from charger's device tree node.

CRs-Fixed: 646414
Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>
Change-Id: I3702a1a9f345797df81cf88d247fcf613c5eb27a