diag: Update the read buffers status properly

Add checks for the logging mode status to mark the buffer
status properly.

CRs-Fixed: 2033760
Change-Id: I29a13e2fecaecacc1a0f46358ae7d4db1d2b3786
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>