USB: u_bam_data: Check for port_usb after fifo allocation

Currently driver allocates memory for data fifo and descriptor fifo for
both pipes before configuring DBM endpoints and doing bam2bam connection
with IPA. There is a chance that disconnect happens and it might race with
previous connect_work. Hence add check after fifos allocation before
confgiuring DBM endpoints and going ahead with bam2bam connections.  Also
check whether request is NULL or not before queuing to USB controller.

Change-Id: I6d5cf8347b7722f512c7d93cd9ab58f0e4e10384
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>