diag: Fail read_work if HSIC channel is suspended

read_work work function continuously keeps queueing IN URBs to
the USB. In suspend scenario, this can lead to transfer ring
getting exhausted and expansion of ring failing. After this
when the target resumes, meaningful read URB submission fails
leading to diag port loss.
Fix this by not invoking diag_bridge_read if HSIC channel is
suspended.

Change-Id: Ic9b76095a00ae7cebe26cded3d95d4c4cb4fb42c
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>