power: smb135x-charger: change the OTG enable sequence

If the OTG was enabled before, the driver is required to
disable and enable OTG to actually re-enable it.

This will address the issue where 5V was not seen after enabling
OTG when an over current interrupt happens.

CRs-Fixed: 794748
Change-Id: I54764ddda2c33aff985196b7be9e317d9b7b45b4
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>