dwc3: gadget: Stop active transfers before stopping USB device controller

Stop all active data transfers before clearing run/stop bit per Synopsys
databook. Hence call dwc3_stop_active_transfers() API before stopping USB
device controller.

CRs-Fixed: 2194063
Change-Id: I21b1556ce2c69cdbed744191d6fabae7a37ae061
Signed-off-by: Mayank Rana <mrana@codeaurora.org>