diag: Prevent real time mode update for multi mode sessions

When on-device logging with multi mode is started real time
voting should not happen. Prevent real time voting if any
PD is in buffering mode after USB disconnect or on-device
logging is stopped.

Change-Id: I66b234cdd4d310f1b4a2fa0080e128eab7835e6c
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>