power: qpnp-smbcharger: Enable parallel charger if input is present

The parallel charger check in the fast-chg handler is only needed
in the enable parallel-charging path. Handle this by checking
for the input presence before configuring the parallel charger.

CRs-Fixed: 1089991
Change-Id: I7a12f62de0b8c36797511bac97ecbb9fbc1caf26
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>