usb: dwc3: gadget: Properly initialize LINK TRB

commit 1200a82a upstream.

On ISOC endpoints the last trb_pool entry used as a
LINK TRB is not getting zeroed out correctly due to
memset being called incorrectly and in the wrong place.
If pool allocated from DMA was not zero-initialized
to begin with this will result in the size and ctrl
values being random garbage. Call memset correctly after
assignment of the trb_link pointer.

Fixes: f6bafc6a ("usb: dwc3: convert TRBs into bitshifts")
Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>