mhi: core: Do not clear transaction status

MHI transaction status stores the OVERFLOW status
received from device.  MHI clients uses this
status to determine overflow buffers, do
not clear the status.

CRs-Fixed: 1042516
Change-Id: Iaaff06c1c39775d6a33ca17851f1e1579b2a2ecb
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>