usb: dwc3: gadget: clear events in top-half handler

Now that all the infrastructure is in place, we can
clear events in the top-half handler in order to
bring IRQ line low ASAP.

This is also a necessary step in order to implement
workaround for known erratum in follow-up patches.

Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Change-Id: Ic0823f85c0386045ab4865544bef0403ec047a99
Git-commit: 65aca3205046d159b2c79f7531203a53aec9cf35
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


[hemantk@codeaurora.org: resolved merge conflict]
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>
Signed-off-by: Mayank Rana <mrana@codeaurora.org>