Revert "smb138x: use chg src bit to disable parallel charger"

This reverts commit 0f0e36134d8a1082f099d543a122cd10d777beda ("smb138x:
use chg src bit to disable parallel charger)

This is not required, since smb1355 support is moved to its own driver.

Change-Id: I1bd454030d29195f03be132d167ec8294169b9d5
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>