USB: dwc3: Fix usb host mode device rebooting in loop issue

USB driver should take care of enabling required clocks for
accessing AHB2PHY register. Currently driver is not enabling
USB core clock before accessing AHB2PHY register during probe,
which is required. This could cause device crash. Hence fix it
by enabling required USB core clock as well before configuring
AHB2PHY register in probe().

CRs-Fixed: 1085406
Change-Id: I9f971cbd54cabbf0119ed00bd811fcf2d7782e05
Signed-off-by: Arumuga Durai A <cadurai@codeaurora.org>