ARM: dts: msm: fix name of 9v parallel current threshold property

The qpnp-smbcharger has a property named
qcom,parallel-usb-9v-min-current-ma. However, this is not included in
the kernel devicetree documentation and it is mistyped as
qcom,parallel-9v-usb-min-current-ma. Add it to the kernel devicetree
bindings documentation and fix the property name so that parallel
charging works with 9V chargers.

CRs-Fixed: 733213
Change-Id: I66d163afd0387950157cc113a6898e49e05c3912
Signed-off-by: Xiaozhe Shi <xiaozhes@codeaurora.org>