bq25710: Report VBUS as 0 when VBUS is too low to measure
bq25710: Report VBUS as 0 when VBUS is too low to measure

BUG=b:124968142
BRANCH=none
TEST=verify VBUS measurement via 'ectool usbpdpower'

Change-Id: I1966537f394016706f96e975c7b54008ea8bfa33
Signed-off-by: Philip Chen <3ee404f9ef892bc3fda6e6a76e65843b5fa44db2@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/1509176
Reviewed-by: Scott Collyer <7d40b3eb9e17bf55d972074a5e77a7ea4159f9dd@chromium.org>
Reviewed-by: Furquan Shaikh <6be5c96c464778f89679b1062a2e0a6af93d2aa5@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec