msm: adsprpc: Fix race condition in internal_control

Protect add and update qos request with mutex to
avoid race condition when multiple threads try to add
or update request simultaneously.

Change-Id: Id33b81bf85246ec69c72bad59cca068e627bb21d
Acked-by: Deepika Singh <dsi@qti.qualcomm.com>
Signed-off-by: Jeya R <jeyr@codeaurora.org>