usb: dwc3: core: Select UTMI clock before core_soft_reset

In HS Only mode of dwc3 controller version 1.9A, UTMI clock needs
to be selected before core soft reset as per the HPG sequence.
Or else the core soft reset fails, leading to enumeration
failure. Hence select UTMI clock before performing
SOFT_RESET operation.

Change-Id: I12d4a992872eecbfc38825282559cd4d592c3896
Signed-off-by: Elson Roy Serrao <eserrao@codeaurora.org>