diag: Handle data ready notification properly

Currently, there is a possibility of nested sleep
during handling of data ready notification to diag
clients. The patch fixes the issue by properly
handling data ready notifications.

Change-Id: Ib30455b41d1b05bff33cc0a627c1fc7e9a1b7568
Signed-off-by: Mohit Aggarwal <maggarwa@codeaurora.org>