USB: OTG: Update vbus_is_on variable for pdata based vbus power routine

vbus power routine can be different based on platform. If vbus power
sequence is provided using platform data(pdata), disconnect of OTG cable
doesn't turn off the VBUS related regulators and required other
interfaces. This issue is seen as vbus_is_on variable remains always zero
for pdata based vbus routine, and msm_hsusb_vbus_power(motg, 0) doesn't
invoke the required vbus power routine. Hence update the vbus_is_on
variable based on return value of pdata based vbus routine. With this
change, it is mandatory that pdata based vbus routine should return the
success/failure result.

CRs-Fixed: 332434
Change-Id: I4c7ce48057f65227b09aac788d0ad24d0f30ed7e
Signed-off-by: Mayank Rana <mrana@codeaurora.org>