usb: ci13xxx_udc: Add mb() before checking req active status bit

Sometimes it is observed that HW is taking some time to update the dTD
fields even after generating interrupt with ENDPTCOMPLETE bit set.
This is causing hw_dequeue fails due to which request completion
handler not called and eventually leads to USB connection lost.

CRs-fixed: 312854
Change-Id: I23fca063ba77ec86f17f866162fab09ae4251bf7
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>