msm: msm-batt: Register the fail-safe voltage with modem

Existing code registers BATTERY_LOW with modem as the
critical voltage where it needs an update. But this is
supposed to be fail-safe voltage. So this change updates
fail-safe voltage inplace of BATTERY_LOW.

CRs-Fixed: 409958
Change-Id: Ie5426619a67a3349d0505c280031be302b898cd3
Signed-off-by: Krishna Vanka <kvanka@codeaurora.org>