dwc3: gadget: Don't block doorbell before halting USB controller

HPG suggests to block ringing of doorbell towards IPA GSI channel
after sending end transfer command and halting USB controller.
Blocking ringing of doorbell before halting USB controller may
result into USB wrapper accessing IPA GSI doorbell register on
setting run/stop next composition switch.

Change-Id: Ie644f8a5afb06bc57cde596d527ffdaa5cf14d35
Signed-off-by: Mayank Rana <mrana@codeaurora.org>