msm: adsprpc: Fix for correct offset calculation

Corrected offset calculation for cache maintenance
operations.

Change-Id: I7a7fc4c4788a1700523ca096c95350fdda7413ba
Acked-by: Deepika Singh <dsi@qti.qualcomm.com>
Signed-off-by: Mohammed Nayeem Ur Rahman <mohara@codeaurora.org>