USB: u_bam: Add check for USB cable connect

It is observed that in case of running compliance suspend/resume
test case with USB 3.0, device is crashing due to trying to use
USB port structure from gbam2bam_data_connect_work() context
which is already freed. Hence add check for port availability
and port->port_usb before trying to access ep IN and ep OUT data
structure in gbam2bam_data_connect_work() to resolve this issue.

CRs-Fixed: 645110
Change-Id: I491dcf07a9c98f63f156a0cc397d3b698d89b6d8
Signed-off-by: Mayank Rana <mrana@codeaurora.org>