usb_bam: wait for UL USB producer pipe to be empty on disconnect

If peer BAM tries to reset its BAM with some pending data
in USB producer BAM then it may cause BAM ERROR_IRQ. Hence, wait
for FIFO to be drained by consumer BAM before disconnecting PIPE.
10msec timeout has been added while waiting which can happen if
peer BAM is stuck and not responding.

CRs-fixed: 702372
Change-Id: I1e67c3674def1d7451ee37a864bdf605d485df04
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>