diag: Free the read workqueue structure to avoid memory leak

The patch frees the read workqueue structure after
scheduled workqueue processes the glink buffers and notifies
glink to avoid possible memory leak.

CRs-Fixed: 2083447
Change-Id: I4e562f9d1cbf02d8306e0a127835af85dfa5db23
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>