dwc3: gadget: Fix dr_mode check with USB device mode APIs

dwc3_gadget_pullup() and dwc3_gadget_vbus_session() APIs are used
to configure USB controller into device mode and start USB gadget.
Current check doesn't allow it if dr_mode is set as peripheral.
Fix this issue by correcting used dr_mode check.

Change-Id: I083b984cb9fa828c37614c7886ab90a4489e8bb1
Signed-off-by: Mayank Rana <mrana@codeaurora.org>