usb: dwc3: fix for the isoc transfer EP_BUSY flag

usb: dwc3: fix for the isoc transfer EP_BUSY flag

commit 9cad39fe4e4a4fe95d8ea5a7b0692b0a6e89e38b upstream.

commit f3af36511e60 ("usb: dwc3: gadget: always
enable IOC on bulk/interrupt transfers") ended up
regressing Isochronous endpoints by clearing
DWC3_EP_BUSY flag too early, which resulted in
choppy audio playback over USB.

Fix that by partially reverting original commit and
making sure that we check for isochronous endpoints.

Fixes: f3af36511e60 ("usb: dwc3: gadget: always enable IOC
		on bulk/interrupt transfers")
Signed-off-by: Konrad Leszczynski <konrad.leszczynski@intel.com>
Signed-off-by: Rafal Redzimski <rafal.f.redzimski@intel.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>