test: host: Fix sbc_charging_v2 test failure
test: host: Fix sbc_charging_v2 test failure

sb_i2c_xfer() assumes 'out' is a valid pointer, which is only true if
out_size is non-zero.

BUG=chrome-os-partner:51207
BRANCH=glados
TEST=`make buildall -j` w/
https://chromium-review.googlesource.com/#/c/342630/

Signed-off-by: Shawn Nematbakhsh <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Change-Id: Ia22dcca2b5318b4d69c7afa49f5c8891ab329bd1
Reviewed-on: https://chromium-review.googlesource.com/342635
Commit-Ready: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Tested-by: Shawn N <5259333ce42e3ace6a73988cec7115ed9d3a661a@chromium.org>
Reviewed-by: Gwendal Grignou <190c5a5edfcf62e0246559bf31fa7548674de3ad@google.com>

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