msm: msm_bus: Fix memory leak during RPM transaction

This is a serious bug that eventually cripples the system due to
lost memory.

CRs-Fixed: 442381
Change-Id: If4d33b35475a33b1602a1d923031345b47af963e
Signed-off-by: Michael Bohan <mbohan@codeaurora.org>
Signed-off-by: Sana Venkat Raju <c_vsana@codeaurora.org>